Figure 1 - CuO₂ plane in high-temperature superconductors.

The blue atoms are copper ions; the green atoms, oxygen. In the experiment, a magnetic copper ion is replaced by either a non-magnetic zinc ion or a magnetic nickel ion (red atom). This influences the spectrum of magnetic excitations measured by inelastic neutron scattering, and also anomalies in the energy–momentum relation of the electrons observed by angle-resolved photoemission. The implication is that magnetic interactions may indeed be responsible for high-temperature superconductivity in these materials.