From BCS to HTS and RTS

Great progress has been made in high temperature superconductivity (HTS) science, material and technology in the 20 years since its discovery. The next grand challenge will be room temperature superconductivity (RTS). Room temperature superconductivity, if achieved, can change the world both scientifically and technologically. Unfortunately, it has long been considered by some to belong to the domain of science fiction and to occur only "at an astronomical temperature and at an astronomical distance". With the advent of HTS in 1987, the outlook for RTS has become much brighter. Currently, there appears to be no reason, either theoretical or experimental, why room temperature superconductivity should be impossible. BCS theory has provided the basic framework for the occurrence and understanding of superconductivity, but, since its inception, it has failed to show where and how to find superconductivity at higher temperatures. To date, empiricism remains the most effective way to discover superconductors with high transition temperatures. In this paper based on the talk given at the Professor Yang's 85^th birthday celebration on October 31, 2007 in Singapore, I shall summarize the search for superconductors of higher T_c prior to and after the discovery of HTS, list the common features of HTS and describe some approaches toward RTS that we are currently pursuing.