Superconductors themselves put out a magnetic field, which is so powerful it can levitate objects, such as trains, allowing them to travel extremely fast. Being able to achieve superconductivity within magnetic fields greatly alters our understanding of the phenomenon, and also opens up new opportunities for superconductive technology. But for a long time, magnetic fields were the enemy of superconductivity. In order for a material to gain superconductivity, the electrons travelling through it need to pair up with electrons of the opposite "spin" - these pairings are known as Cooper pairs. Once paired up with a buddy, electrons can easily travel along a material without causing resistance, instead of rattling around as individual electrons do.