Electron Superconductors Challenge Theories, Start a New Race

Just when discoveries of superconductors having critical temperatures up to 70–80 K had ceased to cause much commotion in the popular press, or to compel researchers to give up their ongoing projects and start studying the new materials, announcement of a new class of 20‐K superconductors in January once again put the superconductivity community on a high alert. In all of the high‐temperature, cuprate superconductors discovered in the past three years, the charge carriers are holes, or vacancies in the valence band. By contrast, in the superconductors announced in January the charge carriers are electrons. The discovery may provide the key to the correct theoretical model for the cuprate superconductors. It might also guide the search for new materials with critical temperatures even higher than the current record of 125 K.