Update on copper oxide superconductors

The early high-{Tc} superconductors Ba{sub 2}YCu{sub 3}O{sub 7} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} remain the most studied for their potential application. The number and variety of new copper oxide superconductors discovered since 1986 is remarkable. Although physicists like to take credit for the superconductivity revolution, it is really a revolution in new materials. New materials of continually increasing complexity have driven the field forward since its beginning. It is no accident that the chemically simplest copper oxide superconductors were discovered first. Higher {Tc} values have been caused by the rapid growth in general knowledge in the material community of the empirical factors necessary for the occurrence of high-{Tc} superconductivity. The growth is based on improving chemical understanding of previous discoveries. The chemical understanding and complexity of cuprate superconductors continue to increase. The appearance in 1993 of mercury-based materials has further raised {Tc} values.