Abstract
We propose a two-dimensional (2D) band structure calculation for alcaline-earth-substituted La2CuO4 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 Tc as a function of the position of the Fermi level (i.e. Cu+++/Cu++ ratio). This model explains the high Tc's observed experimentally and the relation between superconductivity and SPT.
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