The high-temperature copper-oxide superconductors, which offer resistance-free current flow at temperatures extending well above 100 K, are formed by doping certain copper-oxide compounds or by adding excess oxygen to them. The parent compounds—all antiferromagnetic insulators—couldn’t be more different from their superconducting offspring: Magnetism and superconductivity are generally antithetical. Yet it’s hard to deny one’s heritage. Many theoretical and experimental studies of high-temperature superconducting materials have turned up hints of coexisting magnetism, especially in weakly doped materials, where stronger parental influence is to be expected. But left unanswered are such questions as whether the magnetic phase competes or cooperates with the superconductivity, and whether the two phases coexist microscopically or form spatially separate phases.
Recent experiments 1 – 5 have given particularly dramatic evidence that the ordered arrangement of spins on the copper atoms seen in the parent compounds is always lurking in the shadows, quick to pop up whenever superconductivity...
