The Most Fascinating Manifestation of Superconductivity
A superconductor is immersed in liquid nitrogen to provide cooling below the critical temperature. A magnet is placed in the air above the superconductor and left there levitating. Nothing but magnetic interaction keeps the magnet from falling down.
At room temperature magnetic field lines from the magnet penetrate the superconductor without restraint. After cooling by liquid nitrogen they get trapped by microscopic inhomogeneities in the superconductor. The trapped magnetic lines then serve as invisible threads holding the two objects together at a certain distance.
When the superconductor is taken out of the liquid nitrogen, its temperature slowly starts increasing. As a result, the superconducting properties weaken, and the levitation force gradually gives way to the gravity.