Charge gap and charge redistribution among copper and oxygen orbitals in the normal state of the Emery model

TL;DR

This study investigates how charge redistribution among copper and oxygen orbitals in cuprate superconductors depends on Coulomb interactions and doping, using the Emery model and cellular dynamical mean-field theory.

Contribution

It reveals the key role of Coulomb repulsion and charge-transfer energy in driving charge redistribution in the Emery model of cuprates.

Findings

Charge transfer from Cu to O increases with Cu electron repulsion.

Charge redistribution correlates with the system's position relative to the metal-insulator boundary.

Charge gap size anticorrelates with oxygen hole content.

Abstract

Unraveling the behavior of the electrons in the copper-oxygen planes of cuprate superconductors remains a challenge. Here we examine the electronic charge redistribution among planar copper and oxygen orbitals and the charge gap using the Emery model in the normal state, solved with cellular dynamical mean-field theory at finite temperature. We quantify the charge redistribution as a function of the onsite Coulomb repulsion on the copper orbitals, the bare copper-oxygen energy difference, and the hole or electron doping. We find that the position relative to the metal to insulator boundary of the Zaanen-Sawatzky-Allen diagram determines the charge redistribution among copper and oxygen orbitals. For a fixed bare Cu-O energy difference, an increase in the Cu electron repulsion leads to a transfer of the electronic charge from Cu to O orbitals. For a fixed charge gap size of the undoped state, as the system evolves from a charge-transfer to a Mott-Hubbard regime, the electronic charge is transferred from Cu to O orbitals. Our findings posit the Coulomb repulsion and the bare charge-transfer energy as key drivers of the microscopic process of charge redistribution in the CuO$_2$ plane. They quantify the anticorrelation between the charge gap size and oxygen hole content. They show that for fixed band-structure parameters, the charge gap and the charge redistribution between Cu and O orbitals provide a way to understand observed trends in cuprates.