The trouble started with a high-temperature superconductor, bismuth strontium calcium copper oxide, but did not stop there. These observations are as counter-intuitive as they are contentious. They observe, reliably, the PME in aluminium cooled to 1.2 degrees above absolute zero. But at higher magnetic fields, the transition to superconductivity is accompanied by positive magnetization. Eventually, though, superconductivity disappears when the applied magnetic field becomes sufficiently large.
Smallness is the key.
The researchers interpret the PME as a property of the surfaces of superconductors. Given that small samples have far more surface, in relation to volume, than larger ones, the PME will be more prominent. The answer is that large samples are made of smaller ones stuck together more or less well. The observation of the PME in bismuth strontium calcium copper oxide depended on its being in a loose, granular state. In general, these small superconductors could shed light on the many remaining mysteries of the superconducting state.