Transition-temperature features of layered superconductors

A model theory for the superconducting transition temperature T-c is derived that is based on a generalized version of the Eliashberg equations taking into account an energy dependence in the electronic density of states N(epsilon). We treat an electronic structure with characteristic two-dimensional character. An analytical expression for T-c obtained for intermediate coupling establishes features of the T-c in the logarithmic van Hove scenario. Results describe the behavior of T-c vs x observed in well-annealed La2-xSrxCuO4 oxides.