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

Abstract

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.