Superconductivity in Alcaline-Earth-Substituted La 2 CuO 4 : A Theoretical Model

We propose a two-dimensional (2D) band structure calculation for alcaline-earth-substituted La 2 CuO 4 in the tetragonal phase. We find a degenerate logarithmic singularity in the electronic density of states, as usual in 2D systems. This leads to an orthorhombic-to-tetragonal structural phase transition (SPT). Using the BCS theory, we calculate the superconducting critical temperature T c as a function of the position of the Fermi level ( i.e. Cu +++ /Cu ++ ratio). This model explains the high T c 's observed experimentally and the relation between superconductivity and SPT.