Band crossing and novel low-energy behaviour in a mean field theory of a three-band model on a Cu - O lattice

Abstract

We study correlation effects in a three-band extended Hubbard model of Cu-O planes within the 1/N mean field approach, in the infinite U limit. We investigate the emerging phase diagram and discuss the low energy scales associated with each region. With increasing direct overlap between oxygen orbitals, t pp > 0, the solution displays a band crossing which, for an extended range of parameters, lies close to the Fermi level. In turn this leads to the nearly nested character of the Fermi surface and the resulting linear temperature dependence of the quasi-particle relaxation rate for sufficiently large T . We also discuss the effect of band crossing on the optical conductivity and comment on the possible experimental relevance of our findings.

Destabilization of the Zhang-Rice singlet at optimal doping

“…The Hamiltonian of a single CuO 4 molecule is Figure 1: Orbital parameters and symmetries used in the article. In this sign convention t pp < 0 is physical [19].…”

“…where P σ = p −x,σ + p −ŷ,σ − p +x,σ − p +ŷ,σ describes the four oxygens around the copper, andn dσ ,n p,iσ are the number operators of the copper and oxygen orbitals. The relevant orbitals and parameters [19] are shown in Figure 1. All 25 states of two holes with opposite spins on the five orbitals are taken into account.…”