Phenomenological BCS Theory of the High-TcCuprates

BCS theory is applied to a model characterized by a pair potential withon-site $\left(V_0\right)$, nearest $\left(V_1\right)$, and next nearest $\left(V_2\right)$ neighbor interactions, and the experimental quasiparticle dispersion of the cuprates. Three ingredients are required for a consistent interpretation of the experimental data concerning the pair state of hole-doped copper oxides: the existence of flat bands, a small repulsive $V_0$, and a slightly dominating attractive $V_2$ of the order of 60–80 meV with a ratio $V_2{/V}_1\approx 1.3-1.5$.