A scale with a faulty calibration shows more than is actually there, and a piece of cheese seems heavier. A similar glitch occurred in measuring superconductivity in nickelates, materials that conduct electricity without resistance under certain conditions. A team led by Zhu measured what fraction of a La4Ni3O10 sample becomes superconducting under pressure and got 81–86%. But when other researchers recalculated the same data using standard methods, they got only 51–59%.
The discrepancy arose from the formula used by the authors of the original study. They divided the measured magnetic moment by the theoretical maximum but failed to account for the fact that the sample does not fully expel the magnetic field — a key condition for a superconductor.
This mistake affects not just one experiment. All previously published values for the superconducting fraction in Ruddlesden–Popper nickelates, obtained with the same method, turned out to be overestimated. And these numbers were used to judge how promising these materials are for superconducting technologies. Now scientists will have to revisit their conclusions and perhaps seek other ways to assess them.
Superconductors completely expel magnetic fields from their interior — a phenomenon known as the Meissner effect. It is usually by this effect that one determines how much of a material has become superconducting.