Orbital mixture effect on the Fermi surface-$T_c$ correlation in the cuprate superconductors --- bilayer vs single layer

Abstract: By constructing $d_{x<sup>2-y<sup>2}-d_{z<sup>2}$ two-orbital models from first principles, we have obtained a systematic correlation between the Fermi surface warping and the evaluated $T_c$ for various bilayer as well as single-layer cuprates. This reveals that smaller mixture of the $d_{z<sup>2}$ orbital component on the Fermi surface leads to both of 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 {\it et al.} [Phys. Rev. Lett. {\bf 87}, 047003 (2001)], and the present result unambiguously indicates that the $d_{z<sup>2}$ mixture is a key factor that determines $T_c$ in the cuprates.