A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. Persistent electric current flows on the surface of the superconductor. This excludes the magnetic field of the magnet (Faraday's law of induction). In effect, the current forms an electromagnet that repels the magnet

A superconductor is a substance that conducts electricity without resistance when it becomes colder than a "critical temperature." At this temperature, electrons can move freely through the material. Superconductors are different from ordinary conductors, such as copper. Ordinary conductors lose their resistance (get more conductive) slowly as they get colder. In contrast, superconductors lose their resistance all at once. This is an example of a phase transition. High magnetic fields destroy superconductivity and restore the normal conducting state. Some examples of superconductors are the metals mercury and lead, ceramics and organic carbon nanotubes.