A. History and Background
The first superconductor was discovered by a Dutch physicist, and his name Heike Kamerlingh Onnes, who is a researcher at Leiden University in 1911. On July 10, 1908, Onnes succeeded in liquefying helium by cooling elements up to 4 Kelvin or -269 Celsius. Then in 1911, Onnes began to study the electrical properties of metals at very cold temperatures, probably due to the hypothesis that high rates of movement of electrons in the phonon. At the time it was known that the resistance of a metal will come down when cooled below room temperature, but no one can know how the lower limit of resistance is achieved when the metal temperature approaches 0 K or absolute zero.
Some expert scientists at that time as William Kelvin predicted that electrons flowing in the conductor will stop when the temperature reaches absolute zero. On the other hand, other scientists, including Onnes estimated that the barriers will disappear in these circumstances. To find out the truth, Onnes then drain current in a very pure mercury wire and then measure the resistance while lowering the temperature. At a temperature of 4.2 K, Onnes was surprised to find that its resistance suddenly disappeared. Current flows through the wire mercury constantly.
superconductors made with the aim to obtain the energy efficiency of each machine that has been made before, it is of course very beneficial in helping every human activities. Imagine if a superconductor can be created and used in the quality of your internet or telephone network, you will get good again without costing so much. Now it's like super-fast trains have used the principle of the superconductor has zero resistance.
Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain material when cooled below a characteristic critical temperature. which means there is no resistance when the electrons moving from one point to the another point.
Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. (http://en.wikipedia.org/wiki/Superconductivity)