Systematics of Tc studied on the basis of the d-p model of cuprate superconductors

Cuprate high-Tc superconductors are known to have several relationships between Tc and structural features. For example, the first found one correlates Tc and the Madelung potential difference between planar Cu and O sites. Another one relates Tc to the relative ratio of hole densities at the planar O and Cu sites. In this work we analyzes the dependences of the strength of superconductivity (SC) on the model parameters of the d-p model. We first transform the d-p model into a Hubbard model which proves to have a k-dependent Coulomb interaction. We apply Kondo's theory of the SC gap in cuprates to our model. The obtained so-called SC strength parameter increases with increase of |εp − εd| on both positive and negative sides of εp − εd due to the increase of effective U; εp and εd are energy levels of O 2p and Cu 3d orbitals in the hole picture referenced to the d9 configuration. The above-mentioned two relationships are explained if εp − εd < 0. When εp − εd < 0, the b2g-type is most stable instead of b1g but the difference is tiny, being not definitive.