The heyday of research into the basic properties of intermetallic superconductors took place between 1950 and 1980. During those years, the number of known superconducting intermetallic compounds (consisting of several metallic and metalloid elements) grew explosively, and superconducting transition temperatures T c were pushed to just over 23 K (Nb 3 Ge). (In comparison, the first superconductor, discovered by Heike Kamerlingh Onnes in 1911, was mercury, with T c = 4.15 K). Research groups all over the world searched for higher and higher T c values. The researchers were motivated by a basic desire to find an intrinsic limiting temperature for this intriguing quantum phase and by a very applied interest in making useful superconducting devices.
By the 1970s, an empirical glass ceiling seemed to have been hit. Transition temperatures were stuck at 23 K, and some theorists proclaimed that higher transition temperatures were not possible. The basic research community...
