This is possible because of how superconductors react to magnetic flux lines. When the s.c. enters its superconducting state it expels all magnetic field lines and so levitates above a magnet. But in a type II s.c., at higher temperatures the magnetic flux is allowed to enter in quantized packets.
If one then brings the s.c. to lower temperatures these flux packets are pinned in position and cannot be moved in or out. So the s.c. will not only levitate above the magnet, but below!
More fun with the same principles
This is a manifestation of the Meissner Effect. When a superconductor reaches a critical temperature (usually very cold, 1 - 70 K) it expels all magnetic field lines. So if you place it on top of a magnet, it will float. It will float on a cushion of magnetic field. Additionally it will experience almost no friction so if you make a circular track of magnets it will levitate around it for quite a long time. And look awesome doing it. That vapour trail isn’t propulsive. It’s just how cold that superconductor is, it’s condensing the air around it.
I don't know how we transfer the experiment to a genuine maglev program (trains or cars) but there must be some way to do it. Maybe it will take cold fusion to bring it to fruition?
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