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C-axis current flow in high temperature superconductor (HTS) tape-shaped wires arises in configurations where the local wire axis is not perpendicular to the local magnetic field, such as in power cables with helically wound HTS tapes. The c-axis critical current density Jcc has been recently found to be orders of magnitude lower than the ab-plane critical current density Jcab. Here we report on Jcc (77 K, sf) values of various YBa2Cu3O7-based (YBCO) tapes with different microstructures. Our results show that the value of Jcc (77 K, sf) decreases significantly with increasing concentration of ab-plane stacking faults in YBCO thin films and that the critical current anisotropy γ = Jcab/Jcc can reach values as high as 2070, implying that in the highest-anisotropy tape, ∼20% of the tape width carries c-axis current in a helically wound power cable. [ABSTRACT FROM AUTHOR]

Cu/amorphous BaTiO3/Cu capacitors were tested for their dielectric properties in the 0.1 Hz–100 kHz range, from room temperature to 350 °C. The amorphous barium titanate dielectric layer was deposited by rf sputtering on water-cooled copper electrodes. The room-temperature dielectric constant is around 18 and the dissipation factor is 3×10-3 at 100 kHz. When increasing temperature the dielectric response displays an important frequency dispersion with the appearance of a marked loss peak at low frequencies. This dispersion is ascribed to electrode polarization effects, as evidenced by measurements performed on various film thicknesses and by using different electrodes. The electrode polarization phenomenon is discussed using a simple space charge model and is shown to be related to mobile oxygen vacancies. [ABSTRACT FROM AUTHOR]

The high-temperature superconductor (HTS) CrossConductor (HTS CroCo) is a modified stacked-tape arrangement, aiming for high current density and easy long-length fabrication. It is intended to be used as a strand for a high current cable in industrial dc applications or large high-field magnets. In order to allow for an economical operation, terminations, joints, and connector parts need to be sufficiently low-resistive to minimize the heat generation and thus the cooling cost. On the other hand, industrial applicability requires reliable and easy-to-use concepts. In this paper, three approaches to fabricate soldered joints and terminations for HTS CroCos are presented and assessed based on resistance measurements at 77 K, self-field. Termination resistances of some tens of nano-Ohms were achieved for the best termination concepts. Additionally, four types of low-resistive  HTS CroCo connectors with bending radii of less than 5 cm are introduced and assessed. For the best connector types, some tens of nano-Ohms were achieved giving rise to a heat generation of less than 1 W at operating conditions. [ABSTRACT FROM PUBLISHER]

We report here the structural and superconducting properties of BiSrCaYCu O superconductors with various x values (0.00 ≤ x≤ 0.50) by using the resistivity and ac susceptibility measurements. It is found that addition of Y does not influence the phase purity of Bi:2212, while c-parameter and orthorhombic distortion are affected. Furthermore, the critical temperatures T( R= 0) are increased from 92 K for Y = 0 up to 106 K by 0.15 of Y, followed by a decrease with increasing Y up to 0.50. It is interesting to note the resistivity of the samples with Y = 0.075 and 0.15 reaching to true zero value only at low dc currents up to 2 mA. Interestingly, the onset temperature of diamagnetism obtained from susceptibility data remains nearly unchanged at 94 K up to Y = 0.30, flowed by a decrease to 86 K at Y = 0.50. The superconducting volume fraction and critical currents are improved by Y addition up to 0.15, followed by a decrease with increasing Y up to 0.50. These results are explained in terms of the effects of excess oxygen, secondary phases, and carrier concentration per Cu ions which are produced by Y addition in Bi:2212 system. [ABSTRACT FROM AUTHOR]

We explore the potential that high critical-temperature (high- Tc) superconducting quantum interference device (SQUID) technology has for magnetic recordings of brain activity, i.e., magnetoencephalography (MEG). To this end, we performed a series of benchmarking experiments to directly compare recordings with a commercial (low- Tc SQUID-based) 306-channel MEG system (Elekta Neuromag TRIUX, courtesy of NatMEG) and a single channel high- Tc SQUID system. The source on which we recorded is a head phantom including 32 artificial current dipoles housed inside a half-spherical shell (courtesy Elekta Oy) for calibrating MEG systems. The high- Tc SQUID magnetometer consisted of a single layer \YBa2\Cu3\O7-x (YBCO) film on a 10 mm $\times$ 10 mm bicrystal substrate with a magnetic field sensitivity of $\sim$40 fT/ $\surd$Hz down to 10 Hz. We recorded serial activations of eight tangential current dipoles located at different depths from the surface of the head phantom. Results indicate that our individual high- Tc SQUID demonstrated signal-to-noise ratios (SNRs) about 7–14 times lower than that of similarly-positioned low- Tc SQUIDs in a commercial MEG system. Only considering single-channel SNR, high- Tc SQUIDs with resolution better than 18 fT/ $\surd$Hz would be required to outperform the low- Tc system for shallow dipole sources. This work demonstrates a proof of principle study for future multichannel high- Tc MEG system development. [ABSTRACT FROM PUBLISHER]

Ultracold atoms in optical lattices have great potential to contribute to a better understanding of some of the most important issues in many-body physics, such as high-temperature superconductivity. The Hubbard model-a simplified representation of fermions moving on a periodic lattice-is thought to describe the essential details of copper oxide superconductivity. This model describes many of the features shared by the copper oxides, including an interaction-driven Mott insulating state and an antiferromagnetic (AFM) state. Optical lattices filled with a two-spin-component Fermi gas of ultracold atoms can faithfully realize the Hubbard model with readily tunable parameters, and thus provide a platform for the systematic exploration of its phase diagram. Realization of strongly correlated phases, however, has been hindered by the need to cool the atoms to temperatures as low as the magnetic exchange energy, and also by the lack of reliable thermometry. Here we demonstrate spin-sensitive Bragg scattering of light to measure AFM spin correlations in a realization of the three-dimensional Hubbard model at temperatures down to 1.4 times that of the AFM phase transition. This temperature regime is beyond the range of validity of a simple high-temperature series expansion, which brings our experiment close to the limit of the capabilities of current numerical techniques, particularly at metallic densities. We reach these low temperatures using a compensated optical lattice technique, in which the confinement of each lattice beam is compensated by a blue-detuned laser beam. The temperature of the atoms in the lattice is deduced by comparing the light scattering to determinant quantum Monte Carlo simulations and numerical linked-cluster expansion calculations. Further refinement of the compensated lattice may produce even lower temperatures which, along with light scattering thermometry, would open avenues for producing and characterizing other novel quantum states of matter, such as the pseudogap regime and correlated metallic states of the two-dimensional Hubbard model. [ABSTRACT FROM AUTHOR]

We present a novel scheme for an unbiased, nonperturbative treatment of strongly correlated fermions. The proposed approach combines two of the most successful many-body methods, the dynamical mean field theory and the functional renormalization group. Physically, this allows for a systematic inclusion of nonlocal correlations via the functional renormalization group flow equations, after the local correlations are taken into account nonperturbatively by the dynamical mean field theory. To demonstrate the feasibility of the approach, we present numerical results for the two-dimensional Hubbard model at half filling. [ABSTRACT FROM AUTHOR]

We present a novel scheme for an unbiased, nonperturbative treatment of strongly correlated fermions. The proposed approach combines two of the most successful many-body methods, the dynamical mean field theory and the functional renormalization group. Physically, this allows for a systematic inclusion of nonlocal correlations via the functional renormalization group flow equations, after the local correlations are taken into account nonperturbatively by the dynamical mean field theory. To demonstrate the feasibility of the approach, we present numerical results for the two-dimensional Hubbard model at half filling. [ABSTRACT FROM AUTHOR]

Besides superconductivity, copper-oxide high-temperature superconductors are susceptible to other types of ordering. We used scanning tunneling microscopy and resonant elastic x-ray scattering measurements to establish the formation of charge ordering in the high-temperature superconductor Bi2Sr2CaCu2O8+x. Depending on the hole concentration, the charge ordering in this system occurs with the same period as those found in Y-based or La-based cuprates and displays the analogous competition with superconductivity. These results indicate the similarity of charge organization competing with superconductivity across different families of cuprates. We observed this charge ordering to leave a distinct electron-hole asymmetric signature (and a broad resonance centered at +20 milli--electron volts) in spectroscopic measurements, indicating that it is likely related to the organization of holes in a doped Mott insulator. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate a very high-energy density and high-temperature stability capacitor based on SrTiO3-substituted BiFeO3 thin films. An energy density of 18.6 J/cm3 at 972 kV/cm is reported. The temperature coefficient of capacitance ( TCC) was below 11% from room temperature up to 200°C. These results are of practical importance, because it puts forward a promising novel and environmentally friendly, lead-free material, for high-temperature applications in power electronics up to 200°C. Applications include capacitors for low carbon vehicles, renewable energy technologies, integrated circuits, and for the high-temperature aerospace sector. [ABSTRACT FROM AUTHOR]

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Cluster dynamical mean field methods are used to calculate the superconductivity-induced changes in the interplane conductivity and Raman scattering cross section of the two-dimensional Hubbard model. When superconductivity emerges from the pseudogap, the superconducting response is found to be diminished in amplitude, broadened, and, in the case of the interplane conductivity, shifted to higher frequency. The results are in agreement with data on high-temperature copper-oxide superconductors indicating that the Hubbard model contains the essential low-energy physics of the pseudogap and its interplay with superconductivity in the cuprates. [ABSTRACT FROM AUTHOR]

Higher energy density makes inductive energy storage more promising than capacitive storage for pulsed power supplies in industrial and military fields. To realize high amplitude of pulsed current and relieve stress of opening switch, this paper proposes a novel inductive pulsed power supply consisting of high-temperature superconducting pulse power transformer and ZnO-based nonlinear resistor. First, working processes and laboratory setup are described in detail. Then, simulation using the software SIMPLORER is built to show major pulse characteristics and comparisons of two different nonlinear resistors. For verifying the feasibility of this mode, high-current testing is carried out and the results show that large amplitude of pulsed current 3 kA with energy transfer efficiency 60% is achieved, and the ZnO-based nonlinear resistor can help to limit the voltage of the opening switch to a small constant below its clamping value as current is interrupted. [ABSTRACT FROM PUBLISHER]

We investigated the temperature (T) variation of the normalized magnetization relaxation rate S and of the corresponding normalized vortex-creep activation energy U* = T/S for YBa2Cu3O7 films containing BaZrO3 nanorods, with the external magnetic field H oriented perpendicular to the film surface. It was found that by increasing the film thickness and using nanodot decorated substrates the high-T S(T) maximum appearing at low H is substituted by a minimum in S(T). As revealed by the analysis of the current density dependence of U*, this behaviour is due to the inhibition of vortex excitations involving double vortex-kinks and superkinks formation in the investigated thick films, owing to the large nanorod splay and pinning energy dispersion. [ABSTRACT FROM AUTHOR]

The next generation of high-field magnets that will operate at magnetic fields substantially above 20 T, or at temperatures substantially above 4.2 K, requires high-temperature superconductors (HTS). Conductor on round core (CORC) cables, in which RE-Ba2Cu3O7-δ (RE = rare earth) (REBCO) coated conductors are wound in a helical fashion on a flexible core, are a practical and versatile HTS cable option for low-inductance, high-field magnets. We performed the first tests of CORC magnet cables in liquid helium in magnetic fields of up to 20 T. A record critical current Ic of 5021 A was measured at 4.2 K and 19 T. In a cable with an outer diameter of 7.5 mm, this value corresponds to an engineering current density Je of 114 A mm-2, the highest Je ever reported for a superconducting cable at such high magnetic fields. Additionally, the first magnet wound from an HTS cable was constructed from a 6 m-long CORC cable. The 12-turn, double-layer magnet had an inner diameter of 9 cm and was tested in a magnetic field of 20 T, at which it had an Ic of 1966 A. The cables were quenched repetitively without degradation during the measurements, demonstrating the feasibility of HTS CORC cables for use in high-field magnet applications. [ABSTRACT FROM AUTHOR]

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature 7* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at 7* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected tight polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (Tc), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders. [ABSTRACT FROM AUTHOR]

We are presenting experimental results on the electrical noise in small titanium hot-electron nanobolometers with the critical temperature above 300 mK. The noise data demonstrate good agreement with the conventional bolometer theory prediction. The. noise is dominated by the thermal energy fluctuations (phonon noise) when the operating temperature is set just a few mK below the superconducting transition. The corresponding noise equivalent power (NEP) is about 3 × 10-18 W/Hz1/2 for the smallest measured device. The relative NEP's for the two devices measured scale roughly as the square root of the device volume as one would expect from the theory. Therefore an additional factor of 2-3 reduction of NEP may be feasible if the length and width of our device are further reduced. The demonstrated combination of the low NEP and the relatively high operating temperature is attractive for submillimeter low-background applications. [ABSTRACT FROM AUTHOR]

Inhomogeneities in any form, affecting either the structural properties as superstructures or the electronic degrees of freedom as stripes, play an essential role in the unusual properties of the cuprates. Bi-cuprates, favored for photoemission studies, are unfortunately prone to structural inhomogeneity and superstructure modulations. We have therefore performed combined STM and high resolution photoemission studies on Bi2− y Pb y Sr2− x La x CuO6+ δ (Pb-Bi2201) for different compositions and identified the contributions due to superstructures beyond the well-known (1×4.7) reconstruction. Since the inclusion of the related scattering vectors gives a nearly perfect image of the experimental Fermi surface, it can be speculated how far such modeling is necessary to understand the spectral lineshape. [ABSTRACT FROM AUTHOR]

On the basis of the model that was successfully applied to KC8, RbC8, and CsC8 about a quarter century ago, we have implemented a quantitative calculation of the superconducting transition temperature T c to find that the observed values for T c in both CaC6 and YbC6 are also reproduced in the model, indicating that the model is a unified one for superconductivity in the graphite intercalation compounds with T c ranging three orders of magnitudes. [ABSTRACT FROM AUTHOR]

The anomalous temperature dependence of the angle resolved photoemission spectra (ARPES) in undoped cuprates is investigated by using a self-consistent approach within the t-J-Holstein model. The cooperative interplay of coupling of the hole to magnetic fluctuations and strong electron–phonon interaction turns out crucial to explain the experimental data. The model is extended to take into account the longer-range hoppings t′ and t′′. The effect is a large anisotropy of the electron–phonon interaction (EPI) leading to a completely different influence of EPI on the nodal and antinodal points in agreement with the experiments. [ABSTRACT FROM AUTHOR]

Finite temperature instantons between meta-stable vacua of correlated electronic system are solved analytically for quasi one-dimensional Hubbard model. The instantons produce dynamic symmetry breaking and connect metallic state with the dual vacua: superconducting (SC) and spin-density wave (SDW) states. The instantons spread along the Matsubara’s imaginary time and possess the structure similar to the coordinate-space solitonic lattices previously discovered in quasi one-dimensional Peierls model. On the microscopic level the inter-vacua excursion is described by mutual transformations between the “resonating quartets” of the couples of electron–hole and Cooper pairs. Spectral properties of the electrons in the “instantonic crystal” reveal pseudo-gap (PG) behavior, with finite fermionic density of states in the center of the PG and “flat-band” outside of it. Analytically derived inverse temperature scaling of the pseudo-gap and the densities of the SC and SDW condensates is discussed in the context of ARPES and STM data in high-Tc cuprates. [ABSTRACT FROM AUTHOR]

We present an extension of the recently proposed dual fermion approach to investigate the superconducting properties of the Hubbard model in two dimensions. From the spin–spin susceptibility, we find a reduction of the Néel temperature compared to results from dynamical mean-field theory (DMFT) calculations due to the incorporation of spatial correlations. We present results for the temperature dependence of the leading eigenvalue of the Bethe–Salpeter equation for the particle–particle channel. In agreement with previous studies, we find singlet d-wave pairing to be the dominant contribution to pairing. We further present first results for the finite-doping phase diagram obtained from the leading eigenvalue of the Bethe–Salpeter equations for the particle–hole and particle–particle channels. [ABSTRACT FROM AUTHOR]

A unified theory for the cuprates and the iron-based superconductors is derived on the basis of common features in their electronic structures, including quasi-two-dimensionality, and the large- U nature of the electron orbitals close to $E_{_{\textrm{F}}}$ (smaller- U hybridized orbitals reside at bonding and antibonding states away from $E_{_{\textrm{F}}}$ ). Consequently, low-energy excitations are described in terms of auxiliary particles, representing combinations of atomic-like electron configurations, rather than electron-like quasiparticles. The introduction of a Lagrange–Bose field is necessary to enable the treatments of these auxiliary particles as bosons or fermions. The condensation of the bosons results in static or dynamical inhomogeneities, and consequently in a commensurate or an incommensurate resonance mode. The dynamics of the fermions determines the charge transport, and their strong coupling to the Lagrange-field bosons results in pairing and superconductivity. The calculated resonance mode in hole-doped cuprates agrees with the experimental results, and is shown to be correlated with the pairing gap on the Fermi arcs. [ABSTRACT FROM AUTHOR]

Temperature dependences of the electrical resistivity measured in different magnetic fields ( B ∥ c, J ∥ ab) of electron doped Nd2− x Ce x CuO4+ δ single crystals with different cerium concentration ( x=0.15, 0.17, and 0.20) and oxygen content ( δ) were studied in a temperature range of 1.8–40 K. It was found that the slope of the upper critical field $(dB_{c2}/dT)|_{T_{c}}$ decreases with the increase of the disorder in the system. So, we can distinguish experimentally d-wave and anisotropic s-wave superconductors. Moreover, the slope of the upper critical field and critical temperature decrease with increase of the disorder parameter like in d-wave superconductors with anisotropic scattering. [ABSTRACT FROM AUTHOR]

On the basis of the model that was successfully applied to KC8, RbC8, and CsC8 about a quarter century ago, we have implemented a quantitative calculation of the superconducting transition temperature T c to find that the observed values for T c in both CaC6 and YbC6 are also reproduced in the model, indicating that the model is a unified one for superconductivity in the graphite intercalation compounds with T c ranging three orders of magnitudes. [ABSTRACT FROM AUTHOR]

The use of high-temperature superconductors (HTS) in some power utility applications requires long lengths of conductors with low AC losses and good mechanical properties. This is typically obtained by making multifilamentary wires with thin filaments. In Powder-In-Tube (OPIT) process, the fabrication of thin filaments is limited by the development of non-uniformities due to "sausaging", shear fracture, and tensile fracture in the oxide core. This work analyses factors that control the uniformity of thin filaments of Bi-2223/Ag superconducting tapes. Some simple theoretical considerations have explained the formation of these types of defects in terms of the stress-dependent mechanical properties of the superconducting powder. Experimental results verify that small roller size and low reduction rates during flat rolling (two factors that reduce die hydrostatic stress component in the powder core) improve the uniformity of these filaments. Tapes with core thicknesses of down to 12-18 /spl mu/m have been manufactured, which exhibit values of critical current density of 31-36 kAcm/sup -2/ (at 77 K and 1 /spl mu/V/cm) for heat treatments of 70-200 h. [ABSTRACT FROM PUBLISHER]

We describe two versions of a simple device that enable the J/sub c/ (B,T,/spl epsi/) characterisation of a <40 mm diameter single loop of HTS tape. The loop is mounted on a cylinder that is slit longitudinally at regular intervals around its circumference. Strain is applied by forcing a conical plug into the tapered bore of the cylinder which expands evenly as a consequence. The strain is measured by a strain gauge glued to the surface of the tape. The advantage of this configuration is that it enables insertion in the small bores of the highest field superconducting magnets and thus permits access to fields levels not easily available in more traditional linear pulling devices. Also the loop configuration is more representative of the coil geometry encountered in magnet applications. Representative data are presented and discussed critically. [ABSTRACT FROM PUBLISHER]

This paper describes recent work at DuPont to extend the high power microwave performance of YBa/sub 2/Cu/sub 3/O/sub 7/ and Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ high-T/sub c/ superconducting (HTS) films. The YBa/sub 2/Cu/sub 3/O/sub 7/ films grown by in-situ off-axis magnetron sputtering using are produced by in-situ off-axis sputtering with radiant substrate heating. The Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films are produced by off-axis sputtering followed by annealing in oxygen and Tl/sub 2/O vapor. The microwave surface resistance and power handling of these films has been measured over a wide range of temperature (20 K to 100 K) using a HTS-sapphire resonator technique. At 70 K, the surface resistance of YBa/sub 2/Cu/sub 3/O/sub 7/ films remains below 65 /spl mu//spl Omega/ (@5.56 GHz) with microwave surface current densities up to 5/spl times/10/sup 6/ A/cm/sup 2/. At 70 K, the surface resistance of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films remains below 200 /spl mu//spl Omega/ (@8.1 GHz) with microwave current densities up to 2/spl times/10/sup 6/ A/cm/sup 2/. [ABSTRACT FROM PUBLISHER]

This paper discusses the results of Booz/spl middot/Allen and Hamilton's investigation of the market acceptance issues which would influence the adoption of high temperature superconducting (HTS) receiver coils for low-field MRI equipment. While HTS receivers could bring distinct advantages in image quality or imaging time, the changing healthcare marketplace, especially for high-end diagnostic imaging equipment, makes adoption problematic. In order to achieve commercial acceptance, HTS coils would have to enable new capabilities or applications, while not violating the marketplace requirements of ease of use, safety, and high reliability. [ABSTRACT FROM PUBLISHER]

A YBa/sub 2/Cu/sub 3/O/sub 7-x/ artificial grain boundary Josephson junction mas fabricated on to a [110] SrTiO/sub 3/ substrate employing a MgO seed layer. YBa/sub 2/Cu/sub 3/O/sub 7-x/ grows mainly oriented (103) on SrTiO/sub 3/ and [001] on the seed layer. An artificial 45/spl deg/ a or b axis tilt or twist boundary can occur according to the orientation of the MgO edge with respect to the [001] in plane direction of the substrate. Josephson junctions of good quality and excellent reproducibility were obtained in microbridges patterned across the grain boundary. Typical features of the phenomenology of high critical temperature superconductor (HTCS) Josephson junction were observed. The maximum value of the I/sub C/R/sub N/ product is of the order of 2-3 millivolts at T=4.2 K and of the order of 50 /spl mu/V at T=77 K respectively. The modulation of the critical current with the external applied magnetic field confirms the Josephson nature of the current in the weak link. [ABSTRACT FROM PUBLISHER]

High-temperature superconducting Josephson junctions and dc SQUIDs were fabricated using a ramp edge-geometry SNS configuration. Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ was used as electrodes and PrBa/sub 2/Cu/sub 3/O/sub 7-x/ as barrier. The I/sub c/R/sub n/ value of the junctions was in excess of 120 /spl mu/V at 75 K. The dc SQUIDs showed a flux modulation depth, /spl part/V//spl part//spl Phi/, over 150 /spl mu/V//spl Phi/, at 75 K. The flux noise of the devices, measured with dc bias currents operated at 75 K, showed a 1/f dependence at low frequency having values below 100 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 / (the best values in the range of 30/spl sim/40 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 /) at 1 Hz and less than 5 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 / in the white noise region. The voltage modulation and magnetic field noise were 37 /spl mu/V and /spl sim/2 pTHz/sup - 1/2 / at 1 kHz for the directly-coupled dc SQUID magnetometers (with a pick-up loop 6 mm/spl times/ 3.5 mm) based on the ramp edge-geometry SNS configuration. [ABSTRACT FROM PUBLISHER]

We have measured the quasiparticle tunneling (QPT) in grain boundary Josephson junctions for different high temperature superconductors. The investigation of the temperature and voltage dependence of the QPT in different applied magnetic fields (from 0 to 12 T) over a wide voltage range provided strong evidence for an insulating barrier with a high density of localized states. The average barrier height /spl phi/ and thickness d of the different materials was extracted from the parabolic background conductance at high voltages. In the low voltage regime we observed a zero-bias conductance peak, that is discussed in terms of spin-flip and Kondo-type scattering at the interface (Anderson-Appelbaum model). [ABSTRACT FROM PUBLISHER]

To meet the specifications of future radar and communication systems we developed a low phase noise microwave oscillator. This feedback oscillator consists of a commercial MESFET-amplifier at room temperature and a LaAlO/sub 3/ dielectric resonator with high temperature superconducting (HTS) shielding at 63 K. The resonator operating at a resonance frequency of 5.6 GHz showed unloaded quality factors in the 10/sup 5/ to 10/sup 6/ range. By means of a strong resonator coupling (|S/sub 21/|=6 dB) and an amplifier gain of 20 dB we obtained an output power of +15 dBm. The phase noise L(f/sub m/) of the oscillator was below the detection limit for offset frequencies beyond 10 kHz. For offset frequencies below 5 kHz measurements revealed perfect L(f/sub m/)/spl prop/f/sub m//sup .3/-behaviour according to the Leeson model. The phase noise was -110 dBc/Hz at 1 kHz offset and -130 dBc/Hz at 10 kHz. This phase noise performance is superior to state of the art SAW- or quartz oscillators for f/sub m/>10 kHz. To further reduce the phase noise performance close to the carrier we investigated the implementation of a phase locked loop (PLL). The long term temperature stability of the oscillator frequency can be enhanced by introducing a central cylinder made from rutile (TiO/sub 2/). We present numerical and experimental results on this compensation. [ABSTRACT FROM PUBLISHER]

A computationally efficient approach to modeling complex high temperature superconductor (HTS) microwave circuits is described which combines two-dimensional electromagnetic solutions of microwave transmission lines, incorporating a phenomenological description of HTS behavior, with conventional commercially available microwave-circuit computer-aided-design software. Internal inductance effects are known to have a substantial impact on the design and implementation of narrowband HTS circuits. Phase velocities and characteristic impedances can be well modeled using a phenomenological description of HTS superconductivity along with a generalized approximate boundary condition and a two dimensional electro-magnetic solution to the waveguiding structure. Resultant parameterized design equations can then be incorporated into standard commercially available microwave-circuit computer-aided-design software. The test case examined in detail was the superconducting channelized receiver delivered by the Naval Research Laboratory to Phase II of the High Temperature Superconducting Space Experiment. Excellent agreement was obtained between measurements made on the demultiplexer and this HTS microwave circuit modeling approach. [ABSTRACT FROM PUBLISHER]

High-T/sub c/ edge-type Josephson junctions usually have ex-situ interfaces, that probably contain damaged layers caused by etching process and/or by exposure to air. The ex-situ interface layer may be an origin of poor reproducibility and uniformity of the device characteristics, as well as an excess interface resistance and a suppression of the critical current. We have developed an in-situ edge preparation process to improve the uniformity and electrical characteristics of the edge junctions. In our in-situ process, the base YBaCuO electrode edge is not exposed to air after the preparation of the edge and subsequently followed by the deposition of a barrier layer and a counter electrode. The in-situ YBaCuO/PrBaCuO/YBaCuO junctions showed larger critical current density (J/sub c/) and normal state conductance (G/sub n/) than the ex-situ junctions. In addition, smaller J/sub c/ and G/sub n/ spreads have been obtained for the in-situ junctions. [ABSTRACT FROM PUBLISHER]

We discuss results of our investigations on ambient noise reduction using localized high-T/sub c/ (HTS) passive magnetic shields. We have quantified our results in terms of shielding factors for ambient noise, and signal-to-noise improvement ratio (SNIR) for source fields. Issues such as the critical fields of our HTS shields and their flux noise are also discussed. The relative merits of this and other noise reduction techniques are discussed vis-a-vis magnetocardiography (MCG) and nondestructive testing (NDT) of materials in an unshielded environment. [ABSTRACT FROM PUBLISHER]

To exploit the sensitivity offered by HTS SQUID systems for detection of deep faults inside conductive samples, a new approach was taken to avoid additional noise sources typical of scanning measurements. The excitation fields are rotated by electronic control which permits one to keep the sample and the system stationary during measurements. Flaws of 10 mm and 40 mm length were detected under 12 mm thick covers of aluminum. The orientation of the flaws was mapped by taking advantage of the anisotropic excitation of eddy currents by the chosen differential coils. This approach is particularly promising for ferromagnetically contaminated samples and radially oriented defects, e.g. originating from rivets. [ABSTRACT FROM PUBLISHER]

For the optimization of the operation of rf-SQUIDs, a high pumping frequency f/sub 0/ and a high quality factor Q of the tank circuit are desirable. For this purpose we used a washer rf SQUID or a current-injection loop SQUID integrated with a modified planar hairpin resonator around the SQUID. On LaAlO/sub 3/ substrates, we measured f/sub 0/ at resonance in the range of about 550 MHz to 1.1 GHz and unloaded quality factors Q/sub 0/ from 4000 to about 6000 using several layouts with different diameters. We found that the coupling coefficient k between the SQUID and the resonator can be estimated from the geometrical parameters of the layout. The requirement k/sup 2/Q>1 can easily be met with our design. Our layouts are very flexible, as they make possible the implementation of various single and multilayer antennas. Using a single layer flux transformer, 13 mm in outer diameter, together with a SQUID in the flip chip technique, we obtained a white flux noise of 50 fT//spl radic/Hz for a 150 pH SQUID. [ABSTRACT FROM PUBLISHER]

We have designed an HTS single-layer planar rf double-hole gradiometer with long and well defined baseline up to 5 mm and small washer areas. We measured a gradient field resolution of about 1 pT/(cm/spl middot//spl radic/Hz) above 10 Hz in an unshielded environment. The gradiometer could be operated placed on a swinging pendulum in the geomagnetic field. This permitted a simple demonstration of a movable SQUID system. We placed a SQUID system on a scanning table and performed two-dimensional eddy-current nondestructive evaluation measurements on realistic samples. [ABSTRACT FROM PUBLISHER]

The excess noise levels in HTS grain boundary Josephson junctions, when expressed as critical current fluctuations |/spl delta/I/sub c/|, vary linearly with I/sub c/ as the temperature changes. By contrast, when the critical current is suppressed by an external magnetic field, the measured fluctuations |/spl delta/I/sub c/| remain nearly constant while L itself undergoes order-of-magnitude changes. This effect, which does not seem to have been widely recognized, is examined with respect to the spatial modulation of the critical current density within the junction. Calculations based on this model are in good agreement with our experimental measurements. In related studies, we measure the excess noise levels between Shapiro steps in a microwave-irradiated junction, and find them to agree with a modified version of the Likharev-Semenov equation for thermal noise. [ABSTRACT FROM PUBLISHER]

Superconductor-Normal-Superconductor (SNS) edge Josephson Junctions (JJs) continue to be a focus of high-T/sub c/ superconductor (HTS) electronics development. The ability to form clean edges in HTS materials is essential for successful SNS edge JJs as well as crossovers and via contacts. We report a novel SNS JJ fabrication process in which a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3/ base electrode/insulator bilayer coated with a polyimide passivation layer is rotated during Ar ion milling through a reflowed photoresist mask to form omnidirectional edges. No sample cooling is used during milling. YBa/sub 2/Cu/sub 2.8/Co/sub 0.2/O/sub 7-/spl delta// normal layers and YLa/sub 0.05/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// counter-electrodes completed the SNS JJ's. Devices fabricated using this polyimide passivation layer have significantly smaller spreads in critical current and resistance than those processed without it. [ABSTRACT FROM PUBLISHER]

High Temperature Superconducting (HTS, e.g. YBCO) microwave devices based on bulk or thin film ferroelectrics (e.g. Strontium Titanate-STO) are studied theoretically and experimentally. YBCO/STO/YBCO parallel-plate resonators and based on bulk single crystal STO are for electrically tunable high power filters, phase shifters and other devices in the frequency band 0.5-2.0 GHz of advanced microwave communication systems. Thin film YBCO/STO Inter-digital Capacitors (IDC), Coplanar Waveguides (CPW) phase shifters/delay lines are also designed and studied experimentally for low microwave power applications. Modelling problems of these devices and microwave losses in ferroelectrics are also discussed. [ABSTRACT FROM PUBLISHER]

The article presents several studies by K. Jin and colleagues and R.-U. He, which reveal the vagueness of high-temperature (Tc) superconductivity through an electronic phase diagram of materials copper oxide perovskites. The study used antiferromagnetic Mott insulator, microscopic scale, and conventional energy-band theory. Results show that linear temperature dependence to spin-fluctuation scattering of carriers is responsible for the carrier-pairing mechanism of superconductivity.

The correct nature of high- T C superconductivity is outlined: (i) the cuprates do not superconduct in their cuprate-planes, but in their BaO, SrO, or interstitial-oxygen regions; (ii) doped Ba2YRuO6 and Sr2YRuO6, ruthenates without cuprate-planes, superconduct in their BaO or SrO layers; (iii) the rutheno-cuprates GdSr2Cu2RuO8 and Gd2− z Ce z Sr2Cu2RuO10 have cuprate-planes which do not superconduct, but superconduct in their SrO layers; (iv) LaFeAsO1− x F x superconducts via its oxygen ions, as do related compounds; and (v) the organic compound κ-[BEDT-TTF]2Cu[NCS]2 superconducts along the S chains of the molecule. In YBa2Cu3O7, the superconductivity is consistent with observations by positive muon spin rotation and with analyses indicating an absence of Cu d-band contribution to the superconductivity. Hence only, the BaO layer superconducts. The superconductivity is s-wave in character (not d-wave), once fluxon depinning has been properly accounted for. The superconducting BaO layers are p-type and adjacent to the n-type cuprate-planes. The hole-pairing is not phononic, but Coulombic. Many experiments can be explained by understanding the characteristics of the high- T C mechanism, which contradicts the theories with d-wave superconductivity in the cuprate-planes. [ABSTRACT FROM AUTHOR]

The author reflects on the theory of high-temperature superconductivity. The author probes angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) presenting accurate picture of the microscopic structure of high-temperature superconductors. The author suggests more research on the theoretical and experimental side to determine kinks in high-temperature super conductors.

Presents a study showing that the conducting carriers (probed by infrared spectroscopy) are strongly coupled to a resonance structure in the spectrum of spin fluctuations (measured by neutron scattering) in high-temperature superconductors. Coupling strength sufficient to account for the high transition temperatures of the copper oxides, highlighting a prominent role for spin fluctuations in driving superconductivity in these materials.

The origins of phase noise in oscillator systems are reviewed. A simple, self-excited 7.5 GHz oscillator incorporating either a conventional metal cavity resonator or a high temperature superconducting (HTS) cavity has been produced. Comparative measurements made at 77 K demonstrate significant improvements in the close-to-carrier noise performance of the oscillator incorporating the HTS cavity; 10 dB at a 10 kHz offset rising to more than 25 dB at a 10 Hz offset. The unloaded Q of the HTS cavity doubled to >10/sup 6/ on cooling from 77 K to 64 K suggesting that further improvements in noise performance could be achieved. [ABSTRACT FROM PUBLISHER]

The article discusses research being done on the thinnest high-temperature superconductor. It reference a study by Jian Wang and Qi-Kun Xues published in the journal "Chinese Physics Letters" in 2012. The researchers examined the superconducting transition temperature of a quasi-2D superconductor and the enhancement of superconductivity by interface engineering.

The article discusses research done on the relation among superconductivity, charge order, and the pseudogap region. It references studies published within the issue by R. Comin and colleagues and E. H da Silva Neto and colleagues, respectively. The findings of the studies are considered a major breakthrough in clarifying the complexity surrounding the cuprate superconductors.

The article discusses the anticipated publication of a study by physicist Robert Laughlin in the Physical Review Letters and Physical Review B containing his research on condensed matter physics as of December 2013, with a focus on the origins of high-temperature superconductivity. Topics include criticisms of Laughlin's research, Laughlin's feud with physicist Philip Anderson, and the Mott insulator state.