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The Jahn-Teller effect (JTE) is defined and the historical background of the Jahn-Teller theorem is briefly discussed. The E direct product Beta system, an electronic doublet coupled to a single mode of vibration, is introduced as an elementary example and is used to illustrate features characteristic of Jahn-Teller systems. The spin resonance of Cu++ in various materials is considered and the particular case of Cu++ in a cubic crystal field is used to introduce the E direct product Epsilon Jahn-Teller system. The linear and quadratic E direct product Epsilon systems are discussed, and the linear case is used to illustrate the appearance of the Berry phase in a quantum system. The role of the Jahn-Teller effect in high-temperature superconductivity is also discussed. In particular, the JTE-based superconductivity theories of Englman et al. (Physica C 169, 314-324 (1990)) and Weber et al. (Physica C 162/164, 307-312 (1989)) are briefly reviewed. The possible roles of the Jahn-Teller effect in C60 (buckminsterfullerene) and superconducting K3C60 are also considered.

YBa2Cu 3O7-x and Tl2CaBa2Cu2O8 high temperature superconducting thin films were utilized to fabricate frequency selective surfaces (FSS) at millimeter-wave frequencies (75-110 GHz). An analytical/numerical model was applied, using a Floquet expansion and the Method of Moments, to analyze bandstop superconducting frequency selective surfaces. Experimental results were compared with the model, and showed a good agreement with resonant frequency prediction with an accuracy of better than 1%. The use of the superconducting frequency selective surfaces as quasi-optical millimeter-wave bandpass filters was also demonstrated.

No evidence has been found to account for the superconductivity in copper materials. However, most researchers believe that this phenomenon results from the anisotropic pairing of electrons with opposite spins. Theories on d-wave coupling have also been forwarded to explain the mechanism.

The feasibility of using high temperature superconducting (HTS) electronic devices and components in satellite communication systems is studied. The High Temperature Superconductivity Space Experiment, which was devised by the National Research Laboratory (NRL) to promote HTS technology, is presented. The initial electronic devices for the program, scheduled for launching into space by 1993 and subjected to intensive testing, have already been delivered to the NRL. Plans for further experiments are outlined.

A melt casting process for fabricating bulk high-temperature superconductors has been developed especially for the bismuth-strontium-calcium-copper-oxide system. The method, which results in conductors of various sizes and shapes, has been tested with the production of rods and hollow cylinders for current leads and current limiters, respectively. The characteristics of the superconducting material produced with the method were discussed.

Image analysis techniques have been applied to YBa2Cu3Ox (YBCO) films prepared on silicon substrates to study their microstructure and superconducting behavior as a function of process parameters. The films, which contain yttria-stabilized-zirconia (YSZ) buffers, were subjected to scanning tunneling microscopy and atomic force microscopy. The observed results confirmed the presence of pinhole creation in the YSZ buffers and microcracking in the YBCO system.

The superconducting properties and flux creep in Nd(1+x)Ba(2-x)Cu3O(7-delta) samples have been quantified to determine the effect of replacing Ba(+2) with Nd(+3). The samples, whose x composition ranged from 0.0 to 0.1, were subjected to critical current density, magnetic relaxation and hysteresis measurements at varying temperatures. The results did not reveal any impact of the Nd substitution on the flux pinning energy.

The characterization of silver-sheathed Bi-2223 superconducting tapes has been carried out. The high-temperature superconducting tapes, which were powder-in-tube processed, were subjected to a microstructural evaluation and critical current density measurements at temperatures ranging from 4.2 K to 77 K and under different applied fields. The current-voltage characteristics of pancake coils built from such conductors were also determined.

The viability of using a superconducting fault current limiter in electric power networks was evaluated. Using a thermo-electromagnetic analysis, the performance of such a device operating at liquid nitrogen temperatures was investigated. The device, whose capacity ratings are 25 kV(rms) and 2000 A(rms), consists of a high-temperature superconducting shield covering a primary winding.

The levitation and lateral restoring force properties of yttrium-barium-copper-oxides were investigated for magnetic coupling applications. The high-temperature superconductors, which were fabricated via the melt-powder-melt-growth technology, were also examined with respect to the homogeneity of their levitation forces. The magnetic coupling's torque transmission behavior was also evaluated.

An experiment on the use of subcooled liquid nitrogen to cryostabilize high-temperature superconductors is reported. The coolant, which is designed to flow through microchannels, is proven to raise both current density and low stabilizer fraction with the stability increase in proportion to the coolant velocity and channel aspect ratio. Such a cooling system, however, leads to a higher pressure drop although this problem may be solved by having the coolant flow transversely to the current.

Radio-frequency superconducting quantum interference devices (SQUID) have been developed from high-temperature epitaxial yttrium-barium-copper-oxide thin films. The SQUIDs, whose Josephson junctions are of the S-N-S type, were fabricated via the local oxygen-ion irradiation process which produce devices that work at liquid nitrogen temperature. With a size equal to 1.4 mm by 1.4 mm, the SQUIDs have a magnetic field sensitivity of 2 pT Hz(super -1/2) at 10 Hz.

The fabrication of high-temperature superconducting thin films made of YBa2Cu3O7 via rapid isothermal processing-assisted metalorganic chemical vapor deposition is presented. The technology deposited the superconductors on bulk gold (Au) foils and gold/silicon (Si) substrates. The results, which quantified the enhanced operation of Au/YBCO/n-Si Schottky diodes at 50 K, indicate that YBCO films on a Au/Si substrate may eventually be used to form superconducting/semiconductor structures.

The mechanism of superconductivity in alkali metal - doped fullereness ramins a fascinating and controversial issue. One powerful probe of this mechanism involves the determination of the shift in transition termperature (δ[T.sub.c] upon isotopic substitution. A series of isotopically substituted [Rb,sub.3[C.sub.60] superconductors, where [C.sub.60] corresponds to [C.sub.60].sup.13], ([C.sub.60].sup.13].sub.05])([C.sub.60].sup.12]).sub.0.5], or ([C.sup.0.55].sup.13].sub.60], was investigated. The δ[T.sub.c] determined for [Rb.sub.3] [C.sub.60.].sup.13 0.7 ± 0.1 K, provides an unambiguous value for the isotope shift in fully substituted fullerene superconductors. The δ[T.sub.c] determined for [Rb.sub.3]([C.sub.0.55].sup.13][C.sub.0.45].sup.12].sub.60]), 0.5 K, is also consistent with simple mass scaling of the [Rb.sub.3][C.sub.60].sup.13] result. However, an intermolecular effect not accounted for in existing theories is demonstrated by the unexpectedly large δ[T.sub.c], 0.9 K, that was observed for the [Rb.sub.3]([C.sub.60].sup.12].sub.0.5 materials. These results to critically assess proposed mechanisms of fullerene superoconductivity., Metal-doped fullerenes represent a fascinating class of superconductors that can exhibit transition temperatures ([T.sub.c]) in excess of 30 K[1-5]. The existence of superconductivity at such surprisingly high temperatures has led [...]

The benefits and constraints arising from the use of high temperature superconductors (HTSC) as field windings of electric motors is studied. The design of a 10,000-hp synchronous motor with an air-gap magnetic field induced by the HTSC is described with respect to the superconducting wire requirements necessary for achieving efficient motor operation and reduced size. Results show that a 50% decrease in motor losses and size is attainable as compared to standard motors of equal rating.

The increasing variety of research topics and categories of superconductors indicates the maturity of this particular field of physics. High-temperature superconductive materials (HTSC) have long been a favorite subject among physicists due to their unique electrical and magnetic properties. Aside from their high transition temperatures, HTSCs also exhibit anisotropy and resistivity. These traits are now the main focus of research for physicists in addition for their search for other useful materials.

Analysis of the many experiments on high-temperature superconductivity indicate several essential aspects of any theory. The conductivity and other transport properties as a function of disorder, temperature, and frequency point to a non-Fermi liquid-like behavior, whereas photoemission experiments and magnetic properties indicate the presence of a Fermi surface in momentum space. To reconcile this apparent contradiction, a new type of electron liquid, called a Luttinger liquid, has been postulated, and the present article aims to show the need for this postulate. Theory and experiment indicate that the suitable phenomenological electronic structure model of the CuO layers is that of the one-band Hubbard model. It is also argued that experiment clearly indicates that interlayer interactions strongly affect the superconducting transition temperature, [T.sub.c], consistent with the fact that no theoretical calculations on two-dimensional Hubbard models have resulted in the prediction of high transition temperatures, and that anyon models are not favored by experiment., A common misapprehension is that the theory of high-temperature superconductivity is in disarray. It may be true that theorists are in disarray, perhaps understandably, in that the situation genuinely is [...]

The oxygen isotope effect on the superconducting transition temperature ([alpha.sub.o]) varies a function of x in [La.sub.2-x][Sr.sub.x][CuO.sub.4] and [La.sub.2-x][Ba.sub.x][CuO.sub.4], with the maximum [alpha.sub.o] values ([alpha.sub.o] [is greater than or equal [...]

An outline is given of one of the many models which have been advanced to explain high temperature superconductivity in the quasi-two-dimensional oxides. In these the compensation ensures that there are free positive holes, formed in the oxygen 2p states, which form 'spin polarons' by orienting neighbouring spins in Cu [3d.sup.9] ions. Two spin polarons then combine to form a spinless pair, which obeys Einstein--Bose statistics. It is shown that a degenerate gas of such entities is a superconductor. If this is a correct model, such pairs (bosons) must exist above the critical temperature ([T.sub.c]). Particular attention is given to the properties of these materials at temperatures above [T.sub.c]. An unresolved problem is whether all, or only some, of the carriers form bosons.

Structural Chemistry and the Local Charge Picture of Copper Oxide Superconductors THE DISCOVERY OF HIGH-TEMPERATURE SUPERCONDUCTIVITY in oxides based on copper and rare and alkaline earths at first caught the [...]

A superconducting transformer with 14 kVA power output is described. Laminated ferromagnetic rings reduce the radial magnetic-field component in the winding area.

Formulae for calculating the resonance frequency and microwave losses in high-temperature superconducting (HTS) periodic coplanar waveguide resonators prepared on ferroelectric/dielectric substrates are obtained and numerically analyzed.

A new study investigates the response of high-temperature thin films to a radio-frequency electromagnetic field.

The epitaxy, surface and crystallinity of YBCO thin films can be enhanced through the use of an ECO buffer layer, and this has been investigated using x-ray diffraction.

The development and testing of trapped field magnets with YBCO bulks of high temperature superconductors is described.

The hysteresis of the grain boundary YBCO Josephson junctions with Au film shunt capacitors has been studied. The YBCO junctions were deposited on STO bicrystal substrates through pulsed laser deposition with a 37 degree misfit angle. Results indicate that hysteresis is kept turned off, as current decreases from the normal resistive high voltage, and until the junction voltage reaches the crossover below where the capacitive resistance becomes dominant. Hysteresis can only be achieved if there is a significant reduction in the kinetic inductance of the bridge and the series resistance connecting the capacitors.

A superconducting magnet with homogeneity up to 14 T at 4.2 K and a magnet bore of 74 mm has been designed and constructed. The magnet will be used as the basis for developing a 600MHz/52 mm magnet system for NMR spectroscopy. The magnet has been built using 2 Nb3Sn and 4 NbTi coils, which generates the main field of 14.1 T at 100 A. It can be operated in either persistent or driven mode. The magnetic field decay has been measured to be 0.1 ppm/hour.

A technique for developing seeded melt growth for YBCO superconductor levitators is presented. The process was developed as a means of achieving one of the most promising application of high temperature superconductivity, the creation of frictionless self-stabilized magnetic bearings. The derived levitators exhibit levitation forces ranging from 16 N and 24 N while suspended above a neodymium-iron-boron permanent magnet at 77 degrees Kelvin.

A two-step procedure for producing Tl-based films on silver tape substrates has been developed. The Ba-Ca-Cu precursors were first deposited on a silver tape from an aerosol and then thallinated in a closed crucible with a source of Tl-oxide pellet. Scanning electron microscopy results indicate the formation of plate-like grains and strong c-axis orientation. The best films had a Tc values higher than 100 K. Pole figure measurements show good (001) bi-axial texturing.

Research shows that the condensation energy of high-transition-temperature superconductors can be quantified by a microscopic model measuring resonant neutron-scattering in material YBa2Cu3O7 at zero temperature. Further research is required to establish the model's quantitative capabilities at temperatures other than zero. Model definition calculations are illustrated.

In the interlayer theory of high-temperature superconductivity, the interlayer pair tunneling energy (similar to the Josephson or Lawrence-Doniach energy) is the motivation for superconductivity. This connection requires two experimentally verifiable identities: the coherent normal-state conductance must be smaller than the 'Josephson' coupling energy, and the Josephson coupling energy must be equal to the condensation energy of the super-conductor. The first condition is well satisfied in the only case that is relevant, [(La,Sr).sub.2] [CuO.sub.4], but the second condition has been questioned. It is satisfied for all dopings in [(La,Sr).sub.2], [CuO.sub.4] and also in optimally doped [Hg(Ba).sub.2], CuO.sub.5], which was measured recently, but seems to be strongly violated in measurements on single crystals of [Tl.sub.2][Ba.sub.2][CuO.sub.6]., The theory that ascribes the phenomenon of high-transition temperature ([T.sub.c]) superconductivity in the cuprates primarily to interlayer coupling(1) correlates electromagnetic coupling along the c axis (that is, perpendicular to the [...]

The method of joining of BSCCO superconductors is proposed for the lengthening of high temperature superconducting wires, screens and other wares. BSCCO original superconducting samples were fabricated using the melt quenching technique with substantial annealing. Results demonstrate that the proposed method provides tight holding of individual superconducting components with minimal reduction in superconducting characteristics.

In-plane aligned a-axis oriented YBa2Cu3O7-x/LaSrGaO4/YBa2Cu3O7-x (YBCO/LSGO/YBCO) heteroepitaxial trilayers have been developed on LSGO (100) substrates. The superconductor-insulator-superconductor edge-like planar sandwich-type junctions have an 84 K superconducting transition temperature and flux flow type I-V characteristics. This is attributed to the junctions' use of a-axis oriented YBCO/LSGO/YBCO trilayers.

When a magnetic field penetrates a type II superconductor, it forms a lattice of thin quantized filaments called magnetic vortices. Resistance, magnetization, and neutron diffraction experiments have shown that the vortex lattice of high-temperature superconductors can melt along a line in the field-temperature plane. The calorimetric signature of melting on this line was observed in a high-accuracy adiabatic specific heat experiment performed on [YBa.sub.2][Cu.sub.3][O.sub.6.94]. The specific heat of the vortex liquid was greater than that of the vortex solid., When the temperature T of a classical type II superconductor is lowered in a constant magnetic field H > 0, it enters a mixed state in which the field partially [...]

With a view to the long term exploitation of the high upper critical fields of high temperature and Chevrel phase superconductors and their use in very high field superconducting magnets, we are making measurements of critical currents on practical versions of these superconductors in very high pulsed magnetic fields; up to 50 T so far. The measurements are made using transport currents in order to simulate, as far as possible, conditions in a magnet. We compare the results with those taken in the highest steady fields available to us; 18 T at present. In this paper we present our latest results and describe how the technique is developing. We also review our attempts to model the mechanisms which give rise to the characteristic function of V(dB/dt) which we observe.

We have investigated normal resistivity, critical current and flux creep properties of high Jc Bi2223 and YBCO superconducting bulks. Based on their experimental results, applicability of the bulk to the superconducting fault current limiting device is discussed. As a result, it was found that Bi2223 bulk has a high resistivity and YBCO has high critical current density. Flux creep characteristics for the Bi2223 suggest that practical stable operation can be achieved to decrease the transport current to 70% of the critical current.

Novel back-side coupling was used to produce high-power high temperature superconducting (HTS) filters. Several 2.88 GHz, 0.7% equal-ripple bandwidth, 2-pole [TE.sub.01] mode filters were fabricated using [Tl.sub.2][Ba.sub.2]Ca[Cu.sub.2][O.sub.8] HTS thin films on 20-rail LaAl[O.sub.3] substrates. The calibrated, measured performance of the filter at 77 K was

Photoemission studies of underdoped superconductors above Tc show an energy gap in the excitation spectrum. In addition, specific heat, electrical resistivity, optical conductivity and spin susceptibility were observed to be temperature dependent. This indirectly confirms the formation of such a gap.

Houston--Alexander Muller and Georg Bednorz knew they'd meet resistance of the intellectual kind when they reported a material with little resistance of the electrical kind 10 years ago. The pair [...]