Electronic properties of the three-band Hubbard model

TL;DR

This paper investigates the electronic structure and transport properties of a CuO2-plane using the three-band Hubbard model and DMFT, revealing insights into optical gaps, Fermi surface shapes, and electron-phonon interactions relevant to high-Tc superconductors.

Contribution

It applies DMFT to the three-band Hubbard model to analyze optical gaps, Fermi surface shapes, and electron-phonon coupling in CuO2 planes, providing results consistent with experiments.

Findings

Optical gap is smaller than charge transfer energy, matching experimental data.

Fermi surface shape depends on hopping parameters, surrounding the M point for certain ratios.

Density-density correlation varies with doping and temperature, affecting electron-phonon coupling.

Abstract

We study the electronic band-structure and transport properties of a CuO2-plane within the three-band Hubbard model. The Dynamical Mean-Field Theory (DMFT) is used to solve the many particle problem. The calculations show that the optical gap Delta_opt is given by excitations from the lower Hubbard band into the so called Zhang-Rice singlet band. The optical gap Delta_opt turns out to be considerably smaller than the charge transfer energy Delta (Delta=ep-ed) for a typical set of parameters, which is in agreement with experiment. For the two-dimensional CuO2-plane we investigated the dependency of the shape of the Fermi surface on the different hopping parameters t_CuO and t_OO. A value t_OO/t_CuO >0$ leads to a Fermi surface surrounding the M point. An additional different static shift of the oxygen energies is also considered to calculate the electronic response due to a displacement of the oxygen atoms given by a frozen phonon. The density-density correlation for the oxygen orbitals is linear in doping for both hole and electron doping but shows a different temperature dependency in the two regimes. In the first case it is temperature independent and increases upon doping, which leads to an increasing electron-phonon coupling for the B_1g-mode in high-Tc superconductors.