Two-orbital view on the origin of the material dependence of Tc in the single-layer cuprates

Using the d(x2-y2)+d(z2) two orbital model of the high T-c cuprates obtained from the first-principle calculation, we show that the material dependence of the Fermi surface shape can be understood by the degree of the mixture between the d(x2-y2) and the d(z)2 orbitals. We explain, through investigating the tightbinding hopping integrals, why some cuprates have square shaped Fermi surface, while others have more rounded ones. From this viewpoint, we explain the experimentally observed correlation between the curvature of the Fermi surface and T-c.