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A full wave characterization of high-temperature superconducting (HTS) microstrip lines and resonators is formulated based on the complex resistive boundary conditions (CRBC) of HTS. A variational approach is used to extend the applicable parameter range of the CRBC.

Grenoble, France - When solid-state physicists produced the first high-temperature superconductors in 1986, the accomplishment was hailed as one of the great scientific discoveries of the century. Until then, superconductivity [...]

The recent progress in understanding of the vortex system behaviour in HTSC gives an evidence for spatial and temporal chaos - vortex glass and vortex diffusion and, on the other hand, an evidence for collective phenomena such as vortex flow. A deterministic temporal chaos - diffusion - is responsible for 1/f like noise generation and for irreversibility. These phenomena are well pronounced in frequency dependence of magnetization. They cannot be explained by Anderson-Kim model of the critical state or any extended model. We suggest a novel concept of the critical state in type II superconductors which is based on the phase transition in the vortex system dynamics. This phase transition represents a transition between the chaotic and correlated transport. The role of pinning, in this concept, is suppressing the collective state creation.

An artificial cuprate compound belonging to the BiSrCaCuO family with eight adjacent Cu[O.sub.2] layers in each building block was deposited on a single crystal of SrTi[O.sub.3] by sequentially imposed layer epitaxy. This compound undergoes a five order of magnitude resistivity drop with an onset near 280 kelvin and an offset at 250 kelvin. It exhibits a diamagnetic variation of susceptibility and magnetization below 290 kelvin. Additional observed features, such as strongly nonlinear conductivity, suggests superconductivity as a plausible explanation of the properties of this compound., The maximum critical temperature [T.sub.c] that can be reached with a superconducting cuprate is still an open question. After the discovery of YBaCuO in 1987, higher values of [T.sub.c] have [...]

The superconducting energy gap of a Bi2Sr2CaCu2O8+x monocrystal has been determined, both parallel and perpendicular to the a-b plane, from the viscous part of the ac-susceptibility (Chi double prime) obtaining values for 2Delta(sub vertical bar)/k(sub B)T(sub c) approximately equal to 4.8-5.2 and 2Delta(sub perpendicular)/k(sub B)T(sub c) approximately equal to 2.7-3.4. These results are found to be in good agreement with point contact measurements carried out on the same sample and with those published in the literature. These results would appear to support theories proposing two gap superconductivity in these materials.

Precision isothermal solution calorimetry was used to determine the standard-state enthalpy of formation of a number of phases in the Y-Ba-Cu-O system. An analysis of the data indicates that Y[Ba.sub.2][Cu.sub.4][O.sub.8] is thermodynamically metastable under ambient conditions. Taken together with the results from previous investigations, these data show that all of the superconducting compounds in the Y-Ba-Cu-O system are thermodynamically metastable at low temperatures., Since the discovery of the phenomenon of superconductivity in mercury at 4 K, by Onnes in 1911, researchers have attempted to synthesize superconducting materials with higher transition temperatures. Superconductivity in [...]

Changes in the quasiparticle tunneling features of YBa2Cu3O7-x/metal Pb, Nb planar and point contact junctions with natural tunnel barriers due to exposure to different temperatures and magnetic fields were investigated. A model involving intrinsic energy gap and high-Tc superconductor critical temperature suppression near the tunneling barrier was used to interpret the results. The presence of low-energy gap-like structures in the various tunnel junction types was ascertained.

The preparation of a hybrid conducting polymer/high temperature superconductor device consisting of polypyrrole-coated microbridge is discussed. The oxidation state of the polymer is altered by electrochemical techniques. The superconductivity is observed to be modulated in a controllable and reproducible fashion by a polymer layer and this is rationalized by the occurence of a superconducting proximity effect within the composite assembly. The hybrid assemblies described are useful in the study of electron- and energy-transfer phenomena.

A high critical current density was obtained in the attempt to pattern microbridges in a superconducting line. Microbridges were patterned as narrow as 200 nanometers by a focused beam process without damaging the superconducting properties. A current density of six times 10(super 8) angstroms per square centimeters at 77 Kelvin was generated leading to a corrected value of 10(super 8) angstroms per square centimeters. These results validates the use of focused ion beam in the fabrication of superconducting devices.

The use of high temperature superconducting transresistance amplifiers in far infrared focal plane arrays is studied. Such amplifiers drive electronic loads. The merits of the superconducting flux flow transistor, a small-sized device that gurarantees optimal gain, low noise, favorable output impedances and reaction times of less than 200 ps over a wide extent of temperature are also discussed.

The use of high temperature superconducting (SC) active antennas for sensing electromagnetic waves is studied. The SC antenna functioned adequately as a detector, together with a corner reflector which enhanced the antenna's sensitivity and directivity. A discussion of its operational characteristics is also presented.

The 3 at.% Cu-doped Mg[B.sub.2] samples are prepared at both low temperature and high temperature. The mechanism of enhancement in the [J.sub.c] of the Cu-doped Mg[B.sub.2] samples has varied distinctly from the grain-boundary pinning to the possible Mg[Cu.sub.2] nanoinclusions pinning as the sintering temperatures increases from low temperature to high-temperature.

Direct Observation of Structural Defects in Laser-Deposited Superconducting Y-Ba-Cu-O Thin Films THE MOST IMPORTANT QUESTION concerning the potential of the new high-superconducting transition temperature ([T.sub.c]) cuprate superconductors for large-scale applications [...]

[C.sub.60] single crystals have been intercalated with CH[Cl.sub.3] and CH[Br.sub.3] in order to expand the lattice. High densities of electrons and holes have been induced by gate doping in a field-effect transistor geometry. At low temperatures, the material turns superconducting with a maximum transition temperature of 117 K in hole-doped [C.sub.60]/CH[Br.sub.3]. The increasing spacing between the [C.sub.60] molecules follows the general trend of alkali metal--doped [C.sub.60] and suggests routes to even higher transition temperatures., The superconducting properties of various materials can be modulated by the application of an electric field, and a variety of field-effect devices have been studied lately (1-9). We recently demonstrated [...]

Superconductors are materials that lose all electrical resistance below a specific temperature, known as the critical temperature ([T.sub.c]). Large-scale applications, for example, in superconducting cables, require materials with high (ideally [...]

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.

This paper presents experimental evidence for scaling and data collapse of the magnetic viscosity (creep) coefficient for type II superconductors. It is demonstrated that, by using appropriate scaling, the creep coefficient versus magnetic field curves observed at different temperatures collapse onto one 'universal' curve. This data collapse suggests a peculiar self-similar structure of the creep coefficient as a function of two variables: magnetic field and temperature. Index Terms--Superconducting hysteresis, creep, type II superconductors, high-Tc superconductors.

Integration of a high-temperature superconductor with a nonlinear dielectric ferroelectric such as strontium titanate, i.e., [SrTiO.sub.3] (STO), has created a new class of electrically tunable low-loss microwave components. We have designed and fabricated frequency and phase agile components using a conductor/ferroelectric/dielectric two-layered microstrip configuration. Some examples of these components are: microstrip ring resonators, local oscillators, edge coupled filters, and phase-shifter circuits. These structures have been fabricated using [YBa.sub.2][Cu.sub.3] [O.sub.7-[Delta]] or gold conductor-based microstrip lines fabricated on lanthanum aluminate ([LaAlO.sub.3]) or magnesium oxide (MgO) substrates coated with an STO thin film. Frequency and phase agility are achieved using the nonlinear dc electric-field dependence of the relative dielectric constant of STO ferroelectric thin film ([[epsilon].sub.rSTO]). In this paper, we will present an assessment of the progress that our group has achieved thus far toward integration of this technology into wireless and satellite communication systems. Index Terms--Ferroelectric, high-temperature superconducting, K-band, Ku-band, microwave, tunable.

The high-temperature copper oxide superconductors are of fundamental and enduring interest. They not only manifest superconducting transition temperatures inconceivable 15 years ago, but also exhibit many other properties apparently incompatible with conventional metal physics. The materials expand our notions of what is possible, and compel us to develop new experimental techniques and theoretical concepts. This article provides a perspective on recent developments and their implications for our understanding of interacting electrons in metals., In a paper published in Science very shortly after the 1986 discovery of high-critical temperature ([T.sub.c]) superconductivity by Bednorz and Muller, Anderson identified three essential features of the new superconductors [...]

The layer-structure cuprates with high superconducting transition temperatures [T.sub.c] exhibit a number of anomalous electronic properties in both superconducting and normal states. These anomalies are ascribed to the existence of independent spectra of excitations for charge and for spin, signaling a collective state, a 'quantum protectorate.', Laughlin and Pines (1) recently introduced the term 'quantum protectorate' to describe certain states of quantum many-body systems with properties that are unaffected by imperfections, impurities, and thermal fluctuations. Examples [...]

Angle-resolved photoemission spectroscopy was carried out on ([La.sub.1.28][Nd.sub.0.6][Sr.sub.0.12])Cu[O.sub.4], a model system of the charge- and spin-ordered state, or stripe phase. The electronic structure contains characteristic features consistent with other cuprates, such as the flat band at tow energy near the Brillouin zone face. However, the tow-energy excitation near the expected d-wave node region is strongly suppressed. The frequency-integrated spectral weight is confined inside one-dimensional segments in the momentum space (defined by horizontal momenta |[k.sub.x]| = Π/4 and vertical momenta |[k.sub.y]| = Π/4), deviating strongly from the more rounded Fermi surface expected from band calculations. This departure from the two-dimensional Fermi surface persists to a very high energy scale. These results provide important information for establishing a theory to understand the charge and spin ordering in cuprates and their relation with high-temperature superconductivity., The stripe phase (1, 2), which has attracted considerable attention in connection with recent neutron-scattering data from Nd-substituted ([La.sub.1.48][Nd.sub.0.4][Sr.sub.0.12])Cu[O.sub.4] (Nd-LSCO) (3), represents a new paradigm for thinking about charge carriers [...]

Inelastic neutron scattering was used to study the wave vector- and frequency-dependent magnetic fluctuations in single crystals of superconducting Y[Ba.sub.2][Cu.sub.3][O.sub.6+x]. The spectra contain several important features, including a gap in the superconducting state, a pseudogap in the normal state, and the muchdiscussed resonance peak. The appearance of the pseudogap determined from transport and nuclear resonance coincides with formation of the resonance in the magnetic excitations. The exchange energy associated with the resonance has the temperature and doping dependences as well as the magnitude to describe approximately the electronic specific heat near the superconducting transition temperature ([T.sub.c])., The parent compounds of the high transition temperature (high-[T.sub.c]) cuprate superconductors are antiferromagnetic (AF) insulators characterized by a simple doubling of the crystallographic unit cells in the Cu[O.sub.2] planes. When [...]

Early in the effort to understand high-transition temperature ([T.sub.c]) superconductors, Lee and Read asked a provocative question: Why is the [T.sub.c] of cuprate superconductors so low (1)? The question stems [...]

Seen in ceramic superconductors, stripes are confounding many theorists but exciting a few as a possible clue to how these materials work Takashi Imai wears his stripes reluctantly. Like hundreds [...]

The phenomenon of high-temperature superconductivity is a beautiful and well-posed scientific problem with many facets. On page 283 of this issue, Li et al. (1) report observing a special kind [...]

If three sightings make a trend, then a controversial theory of high-temperature superconductivity may have become a little more chic. The 'stripes' theory states that current flows without resistance along [...]

Issues are presented concerning the superconducting properties of magnesium diboride at temperatures of 39 Kelvin. The research which has been carried out worldwide into high temperature superconductors is discussed.

The Discovery of a Class of High-Temperature Superconductors HIGH TRANSITION TEMPERATURE SUPERCONDUCTIVITY IN the Ba-La-Cu oxide system (1) was discovered by Bednorz and Muller at the IBM Zurich Research Laboratory [...]

New research has indicated that it is possible to measure the short-term phase-coherence properties of high-Tc materials. The researchers were able to measure the frequency-dependent conductivity, which links the alternating currents flowing in the superconductor with an applied alternating electric field. The coherent time-domain spectroscopy technique developed in earlier research has now been made into a strong tool for investigating the frequency range of 100 GHz to 600 GHz.

Twelve years after the original discovery of superconductivity above 30 K in a cuprate material, and despite its subsequent achievement at temperatures ranging up to 160 K in a vast [...]

Ten years ago, the materials now known as high-transition-temperature (high [T.sub.c]) superconductors were discovered. It was a scientific breakthrough of breathtaking proportions which quickly won the Nobel Prize for discoverers [...]

Ten years have passed since the discovery of the high-transition temperature ([T.sub.c]) superconductors. Although there has been no agreement on a complete theory, a consensus has formed that the strong [...]

Previous research has revealed the existence of various layered perovskite-type cuprates containing two-dimensional copper oxide planes. A new family of layered cuprates is reported. The structural, electrical, magnetic and point defect properties of the new perovskite family are investigated. Results indicate that the structure of the new cuprates are strikingly similar to other perovskite families.

When Georg Bednorz and Alex Muller discovered high-temperature superconductivity (HTS) 10 years ago at IBM's research labs near Zurich, newspapers, magazines, and TV news reports across the world were soon [...]

Nine years after the discovery of high-temperature superconductors, attempts to explain how electricity races through these complex crystals without resistance still meet a great deal of resistance themselves. Life was [...]

High-temperature superconductivity researchers are a skeptical bunch. But they can be drawn in by a good mystery. And at the Seventh Conference on Superconductivity and Applications earlier this month in [...]

Researchers have yet to confirm the superconductive traits exhibited by some copper oxide superconductors at temperatures over 200 K. The superconductive traits were only temporary and usually disappeared after several thermal cycles.

To the community of researchers fashioning new high-temperature superconductors (HTSs), 127 degrees Kelvin was starting to look like a permanent barrier. Since 1988, when researchers reported a thallium-based material with [...]