Strong Coupling Diagram Technique for the Three-Band Hubbard Model

TL;DR

This paper develops a strong coupling diagram technique to analyze the three-band Hubbard model relevant for high-temperature cuprate superconductors, deriving equations for hole Green's functions and calculating the energy spectrum.

Contribution

It introduces a self-consistent method for solving the three-band Hubbard model using a truncated series expansion, providing insights into the electronic structure of cuprates.

Findings

Energy spectrum includes Hubbard subbands, oxygen bands, and Zhang-Rice states.

Spectrum exhibits pseudogaps near Hubbard transition frequencies.

Results align with known features of high-$T_c$ cuprates.

Abstract

Using the strong coupling diagram technique equations are derived for hole Green's functions of the three-band Hubbard model, which describes Cu-O planes of high-$T_c$ cuprates. The equations are self-consistently solved in the approximation, in which the series for the irreducible part in powers of the oxygen-copper hopping constant is truncated to two lowest-order terms. For parameters used for hole-doped cuprates the calculated energy spectrum consists of lower and upper Hubbard subbands of predominantly copper nature, oxygen bands with a small admixture of copper states and the Zhang-Rice states of mixed nature, which are located between the lower Hubbard subband and oxygen bands. The spectrum contains also pseudogaps near transition frequencies of Hubbard atoms on copper sites.