A superconductor exhibits zero electrical resistance when cooled below a critical temperature (Tc). It also shows something called the Meissner effect – the expulsion of magnetic field lines from the interior of the superconductor as it is cooled to below Tc. So superconductors are also powerful electromagnets.
The demo in Lecture 3 had a copper-oxide based superconductor cooled by liquid nitrogen and placed above a track of magnets. This led to that nice levitation above the magnetic track. The superconductor was based on the solid-state material YBa2Cu3O7 (which I studied during my PhD in the late 1980s !), and was the first compound to have a Tc above 90K.