Orbital mixture effect on the Fermi-surface-Tc correlation in the cuprate superconductors: Bilayer vs. single layer

By constructing d(x2-y2) - d(z2) two-orbital models from first principles, we have obtained a systematic correlation between the Fermi surface warping and theoretically evaluated T-c for various bilayer as well as single-layer cuprates. This reveals that a smaller mixture of the d(z2) orbital component on the Fermi surface leads simultaneously to larger Fermi-surface warping and higher T-c. The theoretical correlation strikingly resembles a systematic plot for the experimentally observed T-c against the Fermi surface warping due to Pavarini et al. [Phys. Rev. Lett. 87, 047003 (2001)], and the present result unambiguously indicates that the d(z2) mixture is one key factor that determines T-c in the cuprates.