Introduction: Superconductivity in Oxides Before 1986

Abstract

First discovered at the beginning of this century, superconductivity was observed initially in metals and binary alloys, then the focus shifted to the study of chalcogenides and, more recently, to organic compounds. Up until 1986, superconductivity was limited to low temperatures and, in particular, it was linked to the use of liquid helium: the highest critical temperature that had been observed was 23.3 K for Nb₃Ge. In spite of this handicap, superconducting materials played a role in electrotechnical applications, especially in the construction of magnets for high fields. These possibilities were then reinforced with the discovery in 1970 of superconducting ternary chalcogenides, which were studied particularly because of their high critical fields [1.1]. Important progress had been made in recent years in fundamental understanding of solid-state physics, not only dealing with the interactions between superconductivity and paramagnetism but also in the field of organic superconductors [1.2–5]. However, an increase in the critical temperature of about 10 K, or even of only a few degrees, appeared unlikely, in spite of the observations made by Little in organic superconductors [1.6]. The discovery in 1986 by Bednorz and Müller [1.7] of superconductivity in copper oxides close to 35 K necessitated drastic revision of previously accepted ideas. Two years after this event, in 1988, critical temperatures as high as 125 K had been reached.