Advances In Superconductivity Viii

Since the discovery of superconductivity with trans1tton temperatures above 77 K, concentrated research activities toward the exploration of practical applica tions of these materials have been carried out. Currently, a remarkable improve ment in superconducting properties has been achieved due to the fine optimization of fabrication processes, and this has attracted industrial interest for future applications. In the case of NdBa Cu 0 materials, a new pinning mecha 2 3 7 nism was found which enhances the critical current under applied magnetic fields. In single crystals of these materials, oxygen control results in an increase in the growth rate. The metalorganic chemical vapor deposition (MOCVD) film quality has been improved by using a new liquid raw material. Simultaneously, real demands from the viewpoint of the market start to be a motivation force, es pecially in electronics application where some products are already being sold. At the same time, interesting physical properlies have been obtained from a new superconducting single crystal which has a layered perovskite structure without copper. In addition, various precision measurement techniques have confirmed the d-wave mechanism and the existence of intrinsicJosephson junctions in single crystals. These new phenomena challenge the existing theoretical models but also open the way for new applications. These significant areas of progress in materials science have led high-Tc super conductivity research into the next phase of activity, while fundamental research continues to be very important. I sincerely hope that this volume will give further impetus to this development.

The field of high-temperature superconductivity has encouraged an inter disciplinary approach to research. It has required significant cooperation and collaboration among researchers, each of whom has brought to it a rich variety of experience from many other fields. Recently, great improvements have been made in the quality of research. The subject has matured and been launched into the next stage through the resonance between science and technology. The current progress of materials processing and engineering in this field is analogous to that previously seen in the development of semiconductors. These include the appearance of materials taking the place of YBa2Cu307 owing to their improved properties (higher critical temperatures and stronger flux pin ning) in which rare earth ions with large radii (La, Nd, Sm) substitute for Y; the development of technology enabling growth control on the nanometer scale; and precise and reproducible measurements that can be used as rigorous tests of theoretical models, which in turn are expected to lead to the develop ment of new devices. For further progress in high-T research, academics and c technologists must pool their knowledge and experience. I hope that this volume will promote that goal by providing the reader with the latest results of high-temperature superconductor research and will stimulate further discussion and collaboration.

The International Symposium on Superconductivity, which has been held annu ally since 1988, is a forum for presenting the most up-to-date information about a broad range of research and development in superconductivity, from funda mental aspects to applications. More than 10 years have passed since the discovery of oxide superconductors and since various developments of applications began. It may be said that the prospects for application of oxide superconductors recently have opened up. Great progress has been made toward practical use, for example, of the flywheel, which uses bulk materials, and the high-performance cryo-cooled magnet made of bismuth wire. These were the results of persistent efforts to develop materials from the viewpoint of materials science and engineering. Also important is the progress in comprehensive understanding of high temperature superconductivity. Unique electronic properties of cuprates such as the non-Fermi liquid normal state, spin-charge separation, spin gap, and d-wave symmetry were discussed at the symposium, as were the unique electromagnetic properties resulting from the low dimensionality of cuprates. In the field of new superconductors, many exotic materials have been discovered since 1986. A decade of work with cuprate superconductors is reviewed in this proceedings, and several of the newest materials are presented. These papers will be instructive for many researchers and for students who are to enter this field.

The 11th International Symposium on Superconductivity was held November 16-19, 1998, in Fukuoka, Japan. Convened annually since 1988, the symposium covers the whole field of superconductivity from fundamental physics and chemistry to new applications. At the 11th Symposium, there was increased interest reported in the development of trial devices using bismuth wires and yttrium-based bulk materials. Among the presentations were those that clearly defined the development targets for next-generation yttrium-based wires and bulk materials and single-flux quantum (SFQ) circuits. Other popular topics were high-temperature superconductivity applications such as SQUIDs, microwave filters, and cryocooler-cooled magnets. With more than 600 participants from 18 countries, the symposium provided an excellent forum for exchanges of the most recent information in the field of superconductivity.

The Seventh International Symposium on Superconductivity brought together researchers at the forefront of all fields such as physics, chemistry, materials, production engineering, and electronic and electrical engineering, once again underlining the interdisciplinary nature of high-temperature superconductivity. Speakers shared their latest findings in the fundamental physics and chemistry; superconductors in the form of individual devices and systems. This comprehensive volume will prove indispensable for all who are involved in high-temperature superconductivity research.

This volume consists of lectures highlighting fundamentals of advances in superconducting materials, related technologies and applications. Theory, fundamental aspects, advances in materials synthesis, processing and properties are featured, as well as current developments of superconducting components and devices.Both HTC and LTC superconducting materials are discussed. Several years after the discovery of high Tc superconductivity and a multinational effort in its study, this book collects the main results on the subject and presents a state-of-the-art view of the correlations between crystal chemistry and physical properties.

This workshop includes about 110 papers describing the flux pinning and related electromagnetic phenomena in superconductors. Various problems are argued on exotic properties of flux lines, flux dynamics, flux pinning mechanisms, critical current density and critical state phenomena in both high- and low-temperature superconductors. Contents:OverviewsFlux Lines, Phase DiagramsIrreversibility Line, Flux DynamicsFlux Spinning Properties, Artificial PinsBulk Materials, Tapes, Thin Films Readership: Researchers and postgraduates students in high Tc superconductivity, condensed matter/solid state physics, applied physics, electrical & electronic engineering and materials science.

C axis Current I ~ . The (11 0) thick homoepitaxial film of 320 nm -------~ ~-=-=--==---==--==--==--- shows a very good surface flatness, which --------·· sJ;1 0] suggests the unique (110) atomic plane helps 2- A [1 1 OJ dimensional epitaxial growth of YBCO films, and shows excellent high Tc. The resultant 1. 0 surface morphology of YBCO is quite different Q ,. -- R(270)=1. 60 m 0 from the (110) heteroepitaxial films of similar 0 0. 0 " thickness [11). In the case of heteroepitaxy ~ . ,,_. 1. 0 irrespective of c-axis [ 12] or a-axis oriented ~ ~. . ,. R(270)=3. 71 m 0 films [5), only thin films show flat surfaces, g 0. 0 . . Tc=92. 3K "' which, however, give usually a degraded Tc due -~ 1. 0 v v I - to lattice mismatching. In conclusion, we have ::1. ,. . . . . R(270)=31. 9 mO succeeded to grow high-quality (11 0) YBCO ~ YBCO film . . Tc=90. 7 K 0. 0 ·;:: YBCO(IIO) 1 0 ·d·--~ YBCO thinfilms on (11 0) YBCO single crystal § substrate ~Xtt=u 1. 0 substra substrates with very flat surfaces and high Tc's. :£ R(270)=40. 1 m 0 0. 0 LLLLL. J. . . . LL~. t-J' L-Tc=9LWO. L-! L-K LLLLL. . . . L. . I. . . . l. . . . L. L. L. J. . . . . L. L. l. . . J 50 100 150 200 250 300 0 ACKNOWLEDGMENTS Temperature (K) One of the authors (T. U. ) would like to thank Fig.