Superconductivity occurs when the natural electrical resistance is exactly 0; it occurs in certain materials at very low temperatures. According to the Cambridge University youtube channel:
The first in a new range of powerful superconductors which could revolutionise the production of machines like hospital MRI scanners and protect the national grid have been developed by engineers at the University of Cambridge. Professor David Cardwell explains what superconductors are, why we need them, and how he and his team have devised techniques to make them more powerful than ever before.