The discovery of high temperature superconductivity has not only opened many possibilities for potential technical applications, but has also provided a unique, challenging research subject for condensed matter physics and material sciences. High temperature superconductivity appears in systems with strong electron correlation and constitutes one of the key issues in condensed matter physics. The understanding of its mechanism will therefore greatly promote the future developments of this branch of science.

During the last ten years great progress has been made in both fundamental and...