Intrasublattice hopping in the extended t-J model and T-c(max) in the cuprates

It is shown that BCS-like scenarios for high-T-c superconductivity based on the extended t-J model yield a characteristic prediction for T-c(max), the critical temperature at optimum doping. A pivotal role is played by t(-) equivalent to t' - 2t '' (t' is the next-nearest-neighbor hopping, t '' is the third-neighbor hopping). Because t(-) determines the shape of the Fermi surface and the nature of saddle points, it strongly affects T-c(max). Owing to symmetry, structural differences outside the CuO2 planes are described exclusively by t(-). This explains semiquantitatively the actual variation of T-c(max) among the various cuprates, with estimated parameters that are consistent with the observed Fermi surfaces.