The BCS pairing theory and the new high T_c oxide superconductors

Abstract

The recent discoveries of the various high-temperature oxide superconductors have given rise to many questions regarding the actual mechanism for the BCS pairing in these materials, beyond the usual phonon-exchange mechanism. In the presence of strong Coulomb correlations and spin fluctuations, there are new theoretical attempts to abandon even the concept of the BCS pairing in these materials. A recent formulation of the BCS pairing approach, suitable for the new materials with layered structures, will be used to discuss various possible phonon and electronic exchange mechanisms. It will be argued that for a quantitative comparison of experimental results with the theoretical predictions of the BCS pairing theory, one has to go beyond the so called “BCS predictions” which are valid only in the framework of an extremely simplified one is still far away from establishing the exact pairing mechanism in these new materials, there is no convincing reason at present to show that the BCS pairing theory will not be applicable to them.