Theory of superconductivity in layered metals

The problem of superconductivity in metals at low temperatures has been of great theoretical interest for a very long time. The first real microscopic understanding of this important process became possible only in 1957, with the development of the well-known BCS pairing theory involving a net dynamical attractive interaction between electrons near the metallic Fermi surface, induced by the phonon-exchange mechanism. It is known for sometime now that the net attractive interaction can also arise from the exchange of suitable electronic excitations in the system. However, with the recent discovery of high-temperature superconductivity in layered cuprates and other oxides, in which the electronic motion in their normal metallic state is highly correlated, many questions have been raised regarding the validity of the generalized pairing theory of superconductivity in such materials. AlternatELTAjj1 will be presented. These are calculated for a general phenomenological model in which both intra-layer and inter-layer couplings of electrons at various conducting layers in each unit cell are included, without specifying the exact exchange mechanism. The effect of an external magnetic field on Tc and the calculation of the temperature-dependence of the upper critical field Hc2 will also be discussed briefly. (author). 18 refs., 3 figs., 1 tab