Superconducting Electronics

This volume is based on the proceedings of the NATO-sponsored Advanced Studies Institute (ASn on The New Superconducting Electronics (held 9-20 August 1992 in Waterville Valley, New Hampshire USA). The contents herein are intended to provide an update to an earlier volume on the same subject (based on a NATO ASI held in 1988). Four years seems a relatively short time interval, and our title itself, featuring The New Superconducting Electronics, may appear somewhat pretentious. Nevertheless, we feel strongly that the ASI fostered a timely reexamination of the technical progress and application potential of this rapid-paced field. There are, indeed, many new avenues for technological innovation which were not envisioned or considered possible four years ago. The greatest advances by far have occurred with regard to oxide superconductors, the so-called high transition-temperature superconductors, known in short as HTS. These advances are mainly in the ability to fabricate both (1) high-quality, relatively large-area films for microwave filters and (2) multilayer device structures, principally superconducting-normal-superconducting (SNS) Josephson junctions, for superconducting-quantum-interference-device (SQUID) magnetometers. Additionally, we have seen the invention and development of the flux-flow transistor, a planar three-terminal device. During the earlier ASI only the very first HTS films with adequate critical-current density had just been fabricated, and these were of limited area and had high resistance for microwave current.

The genesis of the NATO Advanced Study Institute (ASI) upon which this volume is based, occurred during the summer of 1986 when we came to the realization that there had been significant progress during the early 1980's in the field of superconducting electronics and in applications of this technology. Despite this progress, there was a perception among many engineers and scientists that, with the possible exception of a limited number of esoteric fundamental studies and applications (e.g., the Josephson voltage standard or the SQUID magnetometer), there was no significant future for electronic systems incorporating superconducting elements. One of the major reasons for this perception was the aversion to handling liquid helium or including a closed-cycle helium liquefier. In addition, many critics felt that IBM's cancellation of its superconducting computer project in 1983 was "proof" that superconductors could not possibly compete with semiconductors in high-speed signal processing. From our perspective, the need for liquid helium was outweighed by improved performance, i. e., higher speed, lower noise, greater sensitivity and much lower power dissipation. For many commercial, medical, scientific and military applications, these attributes can lead to either enhanced capability (e.g., compact real-time signal processing) or measurements that cannot be made using any other technology (e.g., SQUID magnetometry to detect neuromagnetic activity).

The science of superconducting electronics was first developed over forty years ago, fifty years after the discovery of superconductivity. Since then, a wide range of applications has emerged, and more are envisaged within this ever expanding and exciting field. SQUIDs, the Josephson Effects and Superconducting Electronics chronicles this development from fundamental principles to the present work with high-temperature superconductors. The book discusses superconductivity, Josephson effects, and detectors of unparalleled sensitivity such as SQUIDs. It punctuates theory with practical discussions on how to harness this new science. This complete guide to the subject is an invaluable resource for graduate students and researchers with a specific interest in this field. It also provides guidance to those working in areas of industry where superconducting electronics could be applied.

With the surprising discovery of superconductivity at temperatures above 100 K, this field was not only brought into the public eye, but also stimulated research in universities, scientific institutions and industry, thus continuing the fascinating development which began with the discovery of the Josephson effect in the sixties. Cryoelectronics has become a special branch of cryophysics and cryotechnics and today plays a prominent role whenever high resolution and precision measurements are required. Motivated by this development, seven years ago scientists working in cryoelectronics in the Federal Republic of Germany felt the necessity for regular meetings allowing a free exchange of ideas and results achieved. Seminars under the title of "Kryoelektronische Bauelemente" were held for the first time at the Physikalisch-Technische Bundesanstalt in Braunschweig in 1982 on the occasion of the 100th anniversary of the birth of Walther MeiBner, a pioneer in superconductivity. Since then, meetings have been held every year at different venues in Germany. It is now felt that the status of this field necessitates a review of the results of the past, a description of the current state of the art, and a discussion of future perspectives. This book, entitled SUPERCONDUCTING QUANTUM ELECTRONICS is a collection of invited lectures and contributions which will inform the reader on the most interesting problems involving fundamentals, sensitive detectors and precision metrology being studied by different groups.

In this book new experimental investigations of properties of Josephson junctions and systems are explored with the help of recent developments in superconductivity. The theory of the Josephson effect is presented taking into account the influence of multiband and anisotropy effects in new superconducting compounds. Anharmonicity effects in current-phase relation on Josephson junctions dynamics are discussed. Recent studies in analogue and digital superconductivity electronics are presented. Topics of special interest include resistive single flux quantum logic in digital electronics. Application of Josephson junctions in quantum computing as superconducting quantum bits are analyzed. Particular attention is given to understanding chaotic behaviour of Josephson junctions and systems. The book is written for graduate students and researchers in the field of applied superconductivity.

Recent research on superconductors with high critical temperature has led to results that were not available when the original German edition was prepared but could be included in the present English edition. This concerns materials based on bismuth and thallium, as well as measurements of low microwave loss. The author would like to thank Mr. A. H. Armstrong for translating the book from German to English in a very dedicated and competent manner. Thanks are also due once again to Springer-Verlag for their generous support and cordial cooperation. Bad Salzdetfurth September 1989 Johann H. Rinken Preface to the German Edition The development of materials which lose their electrical resistance when cooled, even before reaching the boiling point of liquid nitrogen, has considerably in creased the interest in superconductor technology, and with it superconductor electronics. This development had not been foreseen when work on the present book started, just over a year ago. Nevertheless, recent results of research on materials with high critical temperature are included to the extent that they seem to be confirmed and to be of interest to superconductor electronics. The present book deals with the physical and technological foundations of superconductor electronics so far as they must be known in order to under stand the principal modes of operation of superconductor electronics components.

Since the discovery of the new copper oxide superconductor in 1987, research groups who were preparing superconductivity electronics got into it. The body of this book contain work of researches in this new field. Some of these research groups originates from the semiconductor research field and the competition and collaboration of them accelerated research activities fortunately.