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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

RF surface resistance of YBa2Cu3O(7-x) thin films

The excitement engendered by the discovery of the new T sub c oxide superconductors has led to much speculation about practical applications of thin films of these materials in digital and analog electronic devices. Most of these envisioned applications involve high frequency signals for which a detailed knowledge of the surface impedance of the novel superconductors is very important. We have measured the surface resistance of thin films of YBaCuO in the frequency range 0.5 less than f less than 17 GHz using a stripline-resonator method. The stripline procedure also was used to measure the surface resistance of high quality gold and aluminum films; the resistance values obtained agree with values predicted from the measured dc resistance using the Pippard formalism for the anomalous skin effect. The YBaCuO were produced by a multilayer deposition process. The films are formed by e-beam evaporation of 24 layers of Y, Ba, and Cu. Films with the highest transition temperature were obtained using yttria-stabilized zirconia (YSZ) substrates. After deposition, the films are transferred to a furnace where they are annealed in flowing O2 at 850 C for 2h. The furnace then is turned off and allowed to cool to 100 C in about 16 h. Auger profiling of the films made by this process shows that the concentrations of Y, Ba, Cu, and O are uniform to within 1 percent throughout the thickness of the film.

Source record↗
NASA NTRS1993

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

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.

Kim, B. F.↗
NASA NTRS1997

Static Test for a Gravitational Force Coupled to Type 2 YBCO Superconductors

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cc. Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating type II, YBCO superconductor, with the percentage change (0.05 - 2.1 %) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10' was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field. Changes in acceleration were measured to be less than 2 parts in 108 of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between static superconductors and gravity.

Li, Ning↗
NASA NTRS1999

Test Status for Proposed Coupling of a Gravitational Force to Extreme Type II YBCO Ceramic Superconductors

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair electron density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (about 10-6 g/cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with the percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 10(exp 4) was reported above a stationary (non-rotating) superconductor. In the present experiments reported using a sensitive gravimeter (resolution <10(exp -9) unit gravity or variation of 10(exp -6) cm/sq s in accelerations), bulk YBCO superconductors were stably levitated in a DC magnetic field (0.6 Tesla) subject to lateral AC fields (60 Gauss at 60 Hz) and rotation. With magnetic shielding, thermal control and buoyancy compensation, changes in acceleration were measured to be less than 2 parts in 10(exp 8) of the normal gravitational acceleration. This result puts new limits on the strength and range of the proposed coupling between high-Tc superconductors and gravity. Latest test results will be reported, along with status for future improvements and prospects.

Noever, David↗
NASA NTRS1999

Granular Superconductors and Gravity

As a Bose condensate, superconductors provide novel conditions for revisiting previously proposed couplings between electromagnetism and gravity. Strong variations in Cooper pair density, large conductivity and low magnetic permeability define superconductive and degenerate condensates without the traditional density limits imposed by the Fermi energy (approx. 10(exp -6) g cu cm). Recent experiments have reported anomalous weight loss for a test mass suspended above a rotating Type II, YBCO superconductor, with a relatively high percentage change (0.05-2.1%) independent of the test mass' chemical composition and diamagnetic properties. A variation of 5 parts per 104 was reported above a stationary (non-rotating) superconductor. In experiments using a sensitive gravimeter, bulk YBCO superconductors were stably levitated in a DC magnetic field and exposed without levitation to low-field strength AC magnetic fields. Changes in observed gravity signals were measured to be less than 2 parts in 108 of the normal gravitational acceleration. Given the high sensitivity of the test, future work will examine variants on the basic magnetic behavior of granular superconductors, with particular focus on quantifying their proposed importance to gravity.

Noever, David↗
NASA NTRS1994

A magnetic shield/dual purpose mission

The objective of this work is to design, build, and fly a dual-purpose payload whose function is to produce a large volume, low intensity magnetic field and to test the concept of using such a magnetic field to protect manned spacecraft against particle radiation. An additional mission objective is to study the effect of this moving field on upper atmosphere plasmas. Both mission objectives appear to be capable of being tested using the same superconducting coil. The potential benefits of this magnetic shield concept apply directly to both earth-orbital and interplanetary missions. This payload would be a first step in assessing the true potential of large volume magnetic fields in the U.S. space program. Either converted launch systems or piggyback payload opportunities may be appropriate for this mission. The use of superconducting coils for magnetic shielding against solar flare radiation during manned interplanetary missions has long been contemplated and was considered in detail in the years preceding the Apollo mission. With the advent of new superconductors, it has now become realistic to reconsider this concept for a Mars mission. Even in near-earth orbits, large volume magnetic fields produced using conventional metallic superconductors allow novel plasma physics experiments to be contemplated. Both deployed field-coil and non-deployed field-coil shielding arrangements have been investigated, with the latter being most suitable for an initial test payload in a polar orbit.

Watkins, Seth↗
NASA NTRS1988

Novel technique to measure the microwave response of high T(c) superconductors between 4.2 and 200 K

This paper describes a novel technique for measurements of the complex surface impedance Z(s) of high-T(c) superconductors over an extremely wide range of temperature, from 4.2 K and at least 200 K. The technique uses a superconducting Pb-plated Cu high-Q-cavity resonator operated at an ambient temperature of 4.2 K, with the sample (typically a 3-mm-diam x 1-mm-thick disk) mounted on a sapphire rod in the center of cavity, at a high B-field and thermally insulated from the cavity walls, making it possible to control the sample temperature externally. Since the cavity characteristics are dominated by the sample properties (the contribution of the Pb-covered walls maintained at 4.2 K is negligible), measurement of the cavity Q and resonant frequency makes it possible to measure Zs as a function of the sample temperature. The Z(s) values for bulk Y1Ba2Cu3O(y) and La(1.85)Sr(0.15)CuO4 were measured over a temperature range 4.2-100 K.

Sridhar, S.↗
NASA NTRS1992

Bulk YBa2Cu3O(x) superconductors through pressurized partial melt growth processing

A novel pressurized partial melt growth process has been developed for producing large pieces of bulk Y-Ba-Cu-O superconductors. During long-time partial melt growth stage, an additional driving force for solidification is obtained by using pressurized oxygen gas. The microstructure and superconducting properties of the resulting samples were investigated. It was found that this new technique can eliminate porosity and inhomogeneity, promote large-scale grain-texturing, and improve interdomain coupling as well.

Hu, S.↗
NASA NTRS1992

X-ray photoelectron spectroscopy characterization of a nonsuperconducting Y-Ba-Cu-O superconductor-normal-metal-superconductor barrier material

A film of a novel nonsuperconducting Y-Ba-Cu-O (YBCO) barrier material was grown using conditions similar to those reported by Agostinelli et al. (1991) for forming a cubic semiconducting (c-YBCO) phase, and the material was characterized using X-ray photoelectron spectroscopy (XPS). A comparison of the XPS spectra of this material to those obtained from the orthorhombic and tetragonal phases of YBCO (o-YBCO and t-YBCO, respectively) showed that the barrier material had spectral characteristics different from those of o-YBCO and t-YBCO, particularly in the O 1s region. Features associated with the Cu-O chain and surface-reconstructed Cu-O planes were absent, consistent with expectations for the simple perovskite crystal structure of c-YBCO proposed by Agostinelli et al.

Vasquez, R. P.↗
NASA NTRS1990

Oxide superconductors under magnetic field

One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of the broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

Kitazawa, K.↗
NASA NTRS1991

Oxide superconductors under magnetic field

One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

Kitazawa, K.↗
NASA NTRS1993

High magnetic field trapping in monolithic single-grain YBa2Cu3O(7-delta) bulk materials

Results of our study on high magnetic field trapping in unirradiated, high quality monolithic single-grain YBa2Cu3O(7-delta) disks are reported. A record high 4 T trapped field at the surface of the unirradiated disks is observed. However, below 11 K, large flux avalanches caused by thermal instability severely limit the remnant trapped field. Therefore, flux avalanche, rather than Jc x d, dictates the maximum trapped field at low temperatures. To overcome this problem, a strong high temperature superconductor trapped field magnet is proposed. A novel application of the avalanche effect is also mentioned.

Gao, L.↗
NASA NTRS1990

Superconductivity applications for infrared and microwave devices; Proceedings of the Meeting, Orlando, FL, Apr. 19, 20, 1990

Various papers on superconductivity applications for IR and microwave devices are presented. The individual topics addressed include: pulsed laser deposition of Tl-Ca-Ba-Cu-O films, patterning of high-Tc superconducting thin films on Si substrates, IR spectra and the energy gap in thin film YBa2Cu3O(7-delta), high-temperature superconducting thin film microwave circuits, novel filter implementation utilizing HTS materials, high-temperature superconductor antenna investigations, high-Tc superconducting IR detectors, high-Tc superconducting IR detectors from Y-Ba-Cu-O thin films, Y-Ba-Cu0-O thin films as high-speed IR detectors, fabrication of a high-Tc superconducting bolometer, transition-edge microbolometer, photoresponse of YBa2Cu3O(7-delta) granular and epitaxial superconducting thin films, fast IR response of YBCO thin films, kinetic inductance effects in high-Tc microstrip circuits at microwave frequencies.

Bhasin, Kul B.↗
NASA NTRS2000

A Dual Polarized Quasi-Optical SIS Mixer at 550-GHz

We describe the design, fabrication, and the performance of a low-noise dual-polarized quasi-optical superconductor insulator superconductor (SIS) mixer at 550 GHz. The mixer utilizes a novel cross-slot antenna on a hyperhemispherical substrate lens, two junction tuning circuits, niobium trilayer junctions, and an IF circuit containing a lumped element 180 deg hybrid. The antenna consists of an orthogonal pair of twin-slot antennas, and has four feed points, two for each polarization. Each feed point is coupled to a two-junction SIS mixer. The 180 deg IF hybrid is implemented using a lumped element/microstrip circuit located inside the mixer block. Fourier transform spectrometer (FTS) measurements of the mixer frequency response show good agreement with computer simulations. The measured co-polarized and cross-polarized patterns for both polarizations also agree with the theoretical predictions. The noise performance of the dual-polarized mixer is excellent, giving uncorrected receiver noise temperature of better than 115 K (DSB) at 528 GHz for both the polarizations.

Chattopadhyay, Goutam↗
NASA NTRS1991

Comparative study of bolometric and non-bolometric switching elements for microwave phase shifters

The performance of semiconductor and high critical temperature superconductor switches is compared as they are used in delay-line-type microwave and millimeter-wave phase shifters. Such factors as their ratios of the off-to-on resistances, parasitic reactances, power consumption, speed, input-to-output isolation, ease of fabrication, and physical dimensions are compared. Owing to their almost infinite off-to-on resistance ratio and excellent input-to-output isolation, bolometric superconducting switches appear to be quite suitable for use in microwave phase shifters; their only drawbacks are their speed and size. The SUPERFET, a novel device whose operation is based on the electric field effect in high critical temperature ceramic superconductors is also discussed. Preliminary results indicate that the SUPERFET is fast and that it can be scaled; therefore, it can be fabricated with dimensions comparable to semiconductor field-effect transistors.

Tabib-Azar, Massood↗
NASA NTRS1991

Comparative study of bolometric and non-bolometric switching elements for microwave phase shifters

The performance of semiconductor and high critical temperature superconductor switches is compared as they are used in delay-line-type microwave and millimeter-wave phase shifters. Such factors as their ratios of the off-to-on resistances, parasitic reactances, power consumption, speed, input-to-output isolation, ease of fabrication, and physical dimensions are compared. Owing to their almost infinite off-to-on resistance ratio and excellent input-to-output isolation, bolometric superconducting switches appear to be quite suitable for use in microwave phase shifters; their only drawbacks are their speed and size. The SUPERFET, a novel device whose operation is based on the electric field effect in high critical temperature ceramic superconductors is also discussed. Preliminary results indicate that the SUPERFET is fast and that it can be scaled; therefore, it can be fabricated with dimensions comparable to semiconductor field-effect transistors.

Tabib-Azar, Massood↗
NASA NTRS1993

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

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.

Garcia, Edouard↗
NASA NTRS1991

The electronic Hamiltonian for cuprates

A realistic many-body Hamiltonian for the cuprate superconductors should include both copper d and oxygen p states, hopping matrix elements between them, and Coulomb energies, both on-site and inter-site. We have developed a novel computational scheme for deriving the relevant parameters ab initio from a constrained occupation local density functional. The scheme includes numerical calculation of appropriate Wannier functions for the copper and oxygen states. Explicit parameter values are given for La2CuO4. These parameters are generally consistent with other estimates and with the observed superexchange energy. Secondly, we address whether this complicated multi-band Hamiltonian can be reduced to a simpler one with fewer basis states per unit cell. We propose a mapping onto a new two-band effective Hamiltonian with one copper d and one oxygen p derived state per unit cell. This mapping takes into account the large oxygen-oxygen hopping given by the ab initio calculations.

Annett, James F.↗