Superconductivity is mostly manifested as the absence of resistance above some critical temperature. It was discovered in 1911. by the Dutch physicist Kamerlingh Onnes in Leiden, 3 years after he first liquefied helium. He measured the resistance of mercury at extremely low temperatures. He began to investigate the electrical properties in metals at extremely cold temperatures. For many years, it was known that as the temperature dropped, so did the resistance of the material, but it was not known what happened at such low temperatures. The electrical resistance of the mercury completely disappeared below the temperature of 4.2K. Like ferromagnetism and spectral lines of atoms, superconductivity is a quantum mechanical phenomenon. The most important characteristic of superconductivity is the Meissner effect - metals cooled to the superconducting state behave like perfect diamagnetics, that is, currents are induced in a thin surface layer that create such a magnetic field that abolish the external field, and the magnetic field inside the superconductor is zero. The superconductivity depends on the temperature , the magnetic field and the current density . If all parameters are below the critical values, the material will be in a superconducting state, otherwise, it will behave like a common metal. Once a superconducting current flows, it will flow forever, without the need for a current source, because due to the lack of resistance there is no loss of energy. For the practical application of superconductors, the temperature at which they become superconductors is important. The problem is that superconductivity occurs only at exceptionally low temperatures, which is a problem in the mass application of superconductors. Therefore, the invention and understanding of materials that would conduct current without resistance at room temperatures is a kind of research problem in the field of solid-state physics.