[en] The authors have set as the objective of this symposium the full-scale evaluation of the present state of research and development in the theoretical fields of superconductivity and new materials; two fields which the entire world's attention is focused and which a great number of researchers are presently putting in their maximum efforts. Their symposium consists of two workshops respectively dealing with superconductivity and new materials. It is needless to say that physical science and material development move forward hand in hand. And they see a recent tendency worldwide that inventions and discoveries in both science and technology are touted fashionably as news topics. The search for new materials that have high critical temperature for use in the field of developing superconductivity has become the focus of social attention around the world. Yet they must not forget that the true important lies in the fundamental study of the mechanism of superconductivity and of its applications. The quantum leap of the Industrial Revolution in England brought forth increased productivity through the development of new technology and locomotive power, eventually leading to the establishment of a new production system, and subsequently, an industrial society in which we live now

[en] This paper reports on the application of superconductors to a variety of power systems and electronic applications that has been pursued over the past twenty years. High-field, high-current type II superconductors such as NbTI and Nb3Sn were successfully applied to a wide range of large-scale applications from bubble chambers to levitated trains. The discovery of the Josephson junction and its associated fast switching behavior was applied to senors, computer logic and a wide range of signal processing applications. It is fair to assume that all of these previous superconducting related applications were compromised by the necessity for liquid helium cooling. The discovery of the high-temperature oxide superconductors has renewed interest and buoyed the prospects for the superconducting technology

[en] Recent results obtained on prototypical metal-semiconductor systems, that is Ag and Pb overlayers on Si(111) as examples of abrupt interfaces and Au films on Si(100) as example of a reactive interface, mostly derived from synchrotron radiation studies, are reviewed in this paper

[en] The transport properties, optical properties and magnetic properties of 2-1-4, 1-2-3 materials and also Bi compounds were measured, and it was found that many of common features were obtained in those physical properties. Especially in the experiments of plasma reflection, a new relation between plasma frequency and critical temperature in all of those materials was obtained. This paper suggests that the same type of carriers are created in these materials and this new type of quasi-particle may be the origin of high temperature superconductivity

[en] This paper reports on a modest concentration of Al dramatically which reduces the upper critical field in single crystals of Ba₂YCu_2.9Al_0.1O₇, increasing two fold in the in-plane coherence length ξ_ab. The resistivity is reduced as well, although not sufficiently to account for the increase in ξ_ab, even in the dirty limit of the standard theory relating microscopic normal-state and superconducting properties. Using the standard theory it is necessary to hypothesize a large change in the Fermi Surface area of Ba₂YCu₃O₇ upon doping to account for the data; this is not especially plausible and may instead indicate that the theory is limited in its applicability to the high-T_c materials

[en] Perhaps the most crucial two problems of the oxide superconductors for the practical application are whether or not breakthroughs are made in improving the critical current significantly and in devising elaborated processes to obtain the desired microstructures to attain the high Jc in the required shape. These two problems seem to be deeply related with the very single factor, high Tc. That is, the problematic characteristics of the high Tc oxides from the materials processing point of view; such as the low carrier density, extremely short coherence length, and rather long penetration depth, seem to be all derived as the result of high Tc. This paper, therefore, is intended to stress the importance to solve these inherent problems with high Tc oxide through the technological efforts. Possible directions towards solving the problems are also discussed

[en] In the entire series of rare earth compounds isomorphic to YBa₂Cu₃O_7-y, only PrBa₂Cu₃O_7-y is not a superconductor. In fact, this material exhibits insulating behavior at all temperatures. Various explanations have been given for this unusual property, the most common being the speculation that in the 1-2-3 structure, Pr may indeed be tetravalent, rather than trivalent as is Y and the other lanthanide substitutions. If this were true, then no excess positive charge would be present in stoichiometric PrBa₂Cu₃O_7-y to produce metallic conduction and hence superconductivity. In order to probe this speculation, we undertook to study the effect of oxygen concentration on the structural and physical properties of PrBa₂Cu₃O_7-y, paying particular attention to possible changes in Pr valency. Throughout most of this paper, unless otherwise indicated, the terms valency and ionicity will be used interchangeably

[en] Situation in the superconducting electronics, the field being developed since mid '60s has changed drastically recently as a result of not only discovery of the high-T_c superconductivity, but also of the nearly simultaneous invention of several novel electronic devices. A detailed analysis of the new situation and prospects of this important field was carried out recently by the present authors of this paper. A complete report on our analysis is being published elsewhere, while in this paper we are presenting a brief summary of its results. The analysis has shown that the virtually only advantage which can arise from applications of the high-T_c superconductors in electronics is a drastic reduction of the refrigeration costs, rather than an improvement of the device performance

[en] Various possibilities depending on the values of material parameters are elucidated based on the effective Hamiltonian derived from Cu:d_x2_-y2 and O:p_σ orbitals in the Cu-O plane of high T_c oxides. In this paper, the region, where RVB of Anderson is expected to be a good starting point, is investigated and theoretical consequences of the mean field approximation of RVB are discussed in comparison with experimental findings. It is argued that RVB will be a reasonable description of the state to support high T_c but that for the description of the onset of superconductivity further studies are necessary

[en] In this paper some fundamental aspects of oxide superconductors are discussed and experiments are suggested. A fundamental problem with the high temperature oxide superconductors is the understanding of the microscopic nature of the superconducting state. The question is what electronic interaction can give rise to this state at such an unfamiliarly high temperature? Since this temperature is much beyond what the BCS superconductivity theory would have predicted and the oxides also have rather unusual normal state properties, there are not surprisingly considerable doubts on whether the traditional BCS view is adequate or appropriate at all when applying to the new materials. This brings many other possibilities into discussions, some of them differ only in names and mathematical appearance, but mostly they can be divided into three classes as will be discussed here