Superconductivity

Superconductivity has always been a very fascinating but difficult problem for theoreticians. It was not till 1957, when an acceptable microscopic theory for this, based on the concept of pairing of electrons of opposite spins and momenta (time-reversed states) near the Fermi surface, was given by Bardeen, Cooper and Schrieffer (BCS). The new high temperature oxide superconductors have given rise to new questions regarding the exact mechanism for BCS pairing in these systems. There are new theoretical models which even abandon the concept of BCS pairing. The aim here, is, however not to discuss these extremely interesting but difficult points but make it purely introductory and simple. In other words, in what follows, the authors only discuss the nature of superconductivity phenomenon and some of the basic important properties of a superconducting material. The presentation of the microscopic theory of the usual superconductors and of the various unusual experimental characteristics and theoretical approaches for the new high-temperature oxide superconductors will be taken up separately