Theory of superconductivity in layered metals

Abstract

The problem of superconductivity in metal at low temperatures has been of great theoretical interest for a very long time. The first real microscopic understanding of this impotant 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. Alternative possibilities for superconductivity in highly correlated cuprates based mostly on the two-dimensional one-band repulsive Hubbard model have been investigated extensively in recent years. In this presentation, it will be argued that superconductivity in highly correlated layered metals can still be understood within a suitably generalized framework of the pairing theory developed by us recently. Explicit results for the transition temperature T_c and the anisotropy of the superconductivity order parameter JJ₁ 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 T_c and the calculation of the temperature-dependence of the uppe critical field H_c2 will also be discussed briefly.