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

By constructing dx2-y2-dz2 two-orbital models from first principles, we have obtained a systematic correlation between the Fermi surface warping and theoretically evaluated Tc for various bilayer as well as single-layer cuprates. This reveals that a smaller mixture of the dz2 orbital component on the Fermi surface leads simultaneously to larger Fermi-surface warping and higher Tc. The theoretical correlation strikingly resembles a systematic plot for the experimentally observed Tc against the Fermi surface warping due to Pavarini et al. [Phys. Rev. Lett. 87, 047003 (2001)], and the present result unambiguously indicates that the dz2 mixture is one key factor that determines Tc in the cuprates.