Are high-temperature superconductors exotic?

High-temperature superconductivity in the copper oxides, first discovered twenty years ago, has led researchers on a wide-ranging quest to understand and use this new state of matter. From the start, these materials have been viewed as 'exotic' superconductors, for which the term exotic can take on many meanings. The breadth of work that has taken place reflects the fact that they have turned out to be exotic in almost every way imaginable. They exhibit new states of matter (d-wave superconductivity, charge stripes), dramatic manifestations of fluctuating superconductivity, plus a key inspiration and testing ground for new experimental and theoretical techniques.