ABSTRACT
The theory of superconductivity developed by Bardeen, Cooper, and Schrieffer (BCS) was founded on a number of assumptions concerning the causes of superconductivity which, on the basis of theory and experiment, were generally agreed. Thus the simplest model which seemed capable of explaining superconductivity was that of a gas of electrons interacting with each other through some two-particle interaction, and this was the model to which Bardeen, Cooper, and Schrieffer addressed themselves. According to the BCS theory the superconductive system possesses an infinite number of macroscopically metastable states characterized by different values of the order parameter which follows slowly varying external fields adiabatically. Dissipative and absorptive processes are caused by the quasi-particles that exists in equilibrium or is created by external fields. The character of these processes is dominated at low temperature by the energy gap, which implies that few quasi-particles are available for absorption.
