History of Superconductivity.

Superconductivity is a state exhibited by many conductors when cooled below their superconducting transition temperatures. Superconductivity is one ofthe most fascinating physical phenomena having a vast potentiality in practical applications. A superconducting material exhibits zero electrical resistivity and complete diamagnetism. The superconducting state is influenced by temperature, magnetic field, and current. There exist critical values for these three parameters above which values the material passes into normal State.

In 1908, the Dutch Physicist Kammerlingh Onnes succeeded in his efforts to liquefy helium, Gaseous helium turned into liquid helium at 4.2K at atmospheric pressure. Using liquid helium as the coolant the variation of  electrical resistance of metals at low temperatures was studied by Chines In one theory, the electrical resistance of pure metals should decrease continuously and vanish at absolute zero temperature. In another theory it was expected to increase exponentially as temperature approaches 0K. However, in the year 1911, onnes discovered that the electrical resistance of highly purified mercury dropped abruptly to zero at 4.15 K. Sudden drop in resistivity was not in accordance with the expectations and was recognized by Onnes to be an emirelynew phenomenon. He called it superconductivity Subsequently super conductivity was discovered in lead. tin, zinc, aluminium and other metals as well as in a number of alloys.