Oxygen hole content, charge-transfer gap, covalency, and cuprate superconductivity

Abstract

Significance Modern theoretical methods solve a long-standing mystery of cuprate high-temperature superconductivity, identifying crucial quantities that optimize the transition temperature. Superconducting cuprates have very different transition temperatures, and even if the optimal value of the superconducting transition temperature is obtained for a given parent compound by varying doping, there is no correlation between optimal doping and transition temperature. Instead, it has been found experimentally that the optimal transition temperature is controlled by oxygen hole content or by the size of the charge-transfer gap. Our calculations show that these two quantities are correlated and that together with covalency they lead to an effective superexchange interaction between copper atoms that ultimately controls the optimal superconducting order parameter.