Discovering superconductors: A path to new science and higher T c 's

Abstract

The search for superconductivity in new and unexpected structures has been ongoing since the initial discovery in Leiden over 9 decades ago. Though the successes are few the rewards are great. Our meeting here today is a direct result of Bednorz and Mueller's discovery of cuprate superconductivity [1]. The questions which have arisen as a result of this single discovery have uncovered inadequacies of theory and stimulated new ways of thinking. Understanding the mechanism(s) of high temperature superconductivity is among the foremost challenges of theoretical and experimental research today [2]. Searching for new superconductors has always been a fruitful research enterprise, and as we see, there are new opportunities for doing so today. For more than 4 decades after the initial discovery there was no microscopic theory (the most outstanding theorists from Heisenberg down tried and failed to come up with a satisfactory theory) and the experimental basis for understanding the underlying mechanisms was inadequate. It must have been a surprise for Kamerlingh Onnes, after taking care to use the purest Hg he could obtain in the investigation that led to the discovery of superconductivity, to find that ordinary solder was also superconducting. In 1932 Meissner discovered barely metallic copper sulfide was superconducting, while high conductivity copper itself was not superconducting. These puzzles and others like it suggested that a comprehensive search for new superconductors might reveal a pattern of occurrence that would reveal clues, and prompted John Hulm and Bernd Matthias, with encouragement from Enrico Fermi [3] in 1951 to undertake a full-scale effort to find new superconductors. This was a propitious time for such an undertaking for a number of reasons. Today parallel reasons exist.