The New 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).

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.

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.

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.

This wide-ranging presentation of applied superconductivity, from fundamentals and materials right up to the details of many applications, is an essential reference for physicists and engineers in academic research as well as in industry. Readers looking for a comprehensive overview on basic effects related to superconductivity and superconducting materials will expand their knowledge and understanding of both low and high Tc superconductors with respect to their application. Technology, preparation and characterization are covered for bulk, single crystals, thins fi lms as well as electronic devices, wires and tapes. The main benefit of this work lies in its broad coverage of significant applications in magnets, power engineering, electronics, sensors and quantum metrology. The reader will find information on superconducting magnets for diverse applications like particle physics, fusion research, medicine, and biomagnetism as well as materials processing. SQUIDs and their usage in medicine or geophysics are thoroughly covered, as are superconducting radiation and particle detectors, aspects on superconductor digital electronics, leading readers to quantum computing and new devices.

The on-going developments, and the recent achievements of the superconducting electronics (especially in the field of Josephson junctions and the inherent nonlinear dynamics) inspired us to organize a conference where different groups working on the subject could meet and discuss the latest results of their investigations. This idea was realized as two joint workshops, the NATO Advanced Research Workshop on Superconducting Electronics with Prof. N.F. Pedersen as chairman, and the 2nd Workshop on Josephson Devices, with Profs. G. Costabile and M. Russo as chairmen, held in Capri, Italy on September 3-7, 1990. The Workshops were very successful. About 70 scientists from 12 countries (Denmark, France, Germany, Greece, Italy, Japan, People's Republic of China, Sweden, United Kingdom, USA, USSR, and Venezuela) enjoyed the many interesting and mostly informal occasions for scientific exchanges as well as the very pleasant weather of Southern Italy. We are very grateful to the Institutions which made possible the realization and the success of the conference with their financial support : NATO Science Committee through the NATO International Scientific Exchange Programmes, University of Salerno, and Istituto di Cibernetica of the Consiglio Nazionale delle Ricerche (C.N.R.) of Italy. The conference was held under the auspices of the Progetto Finalizzato "Superconductive and Cryogenic Technologies" of C.N.R. Finally special thanks go to our Conference Secretary Anna Maria Mazzarella for carrying out most of the organizative work, and for her continuous "on stage" support in solving all the problems which inevitably arise in such occasions.

The title discusses mainly weak superconductivity, in particular the foundations of Josephson effects and their applications in superconducting devices and circuits. One of the most prominent topics in low temperature study, Superconductivity, is presented by the renowned scientist Rudolf Gross, Director of the Walther-Meissner-Institute for Low Temperature Research in Garching, Munich, and his two fellow scientists."