Introduction

Materials form the foundation of most scientific and technological endeavors. This is particularly true for superconductivity research and development. The discovery and perfection of a new class of superconductors invariably leads to the development of new physics and/or new technology. Examples abound. For instance, today’s powerful magnetic resonance imaging technology for medical diagnoses and the omnipotent accelerator technology for exploring the deep secrets of the universe would not have been possible without the perfection of Nb-Ti and Nb3Sn in the 1960s and 1970s, although these are superconductors with low Tc. It was the study on the transition metal dichalcogenides for possible high Tc in the 1970s that led to the discovery of charge density waves, which have become an important subfield of physics. The discovery of high temperature superconductivity in 1986 has created an exciting subfield of physics and promised a new vista in science and technology.