1. High-temperature superconductors

1.1 Properties of superconductors

A superconductor is a material that conducts electric current without resistance below a certain "critical" temperature (T _c ). Unlike ordinary metals, which are subject to the Joule effect, there is no dissipation of energy when a direct current flows through a superconductor: it is a perfect conductor, and its electrical resistance is zero. When cooled to below T _c in the presence of a magnetic field, the latter is expelled from the material. It is a perfect diamagnetic material, and magnetic induction B is zero in its volume. Perfect conduction and diamagnetism are therefore the two generic properties of a superconductor, which manifest themselves when it...