How electrons in high-temperature superconductors pair up and conduct electricity without dissipation is one of the most challenging issues in physics—and one of the most exciting. In that respect, the 2008 discovery of high-temperature superconductivity in a class of materials based on iron1 was among the most significant breakthroughs in condensed-matter research in the past two decades.
Suddenly, in addition to the famous cuprate superconductors, researchers had a second class of materials exhibiting the macroscopic quantum phenomenon of superconductivity at high temperatures (see the article by Charles Day, Physics Today, August 2009, page 36). The road to room-temperature superconductivity appeared smoother because of the chance to compare the two systems.
In conventional superconductors, such as lead or mercury, electrons Bose condense at temperatures of a few kelvin after binding into Cooper pairs. The polarization of the crystal lattice of positively charged ions provides the attractive force between...
