Antiferromagnetism in three-band Hubbard model: Local-ansatz approach

Abstract

The ground state of the three-band Hubbard Hamiltonian for Cu02 planes of high-T, superconductors is investigated. Correlations between holes are included by a local-ansatz approach which starts from the Hartree-Fock approximation and emphasizes the local character of hole correlations. It is found that the hole distribution within Cu02 planes and the region of stability of an antiferromagnetic {AF) ground state are significantly modified by hole correlations. At the filling of one hole per Cu02 unit, and for realistic parameters, the ground state exhibits an AF long-range order. Taking into account the effect of quantum fluctuations, the magnetic moment amounts to 0.47pw hich agrees very well with the experimental value for La2Cu04. The order parameter decreases with doping and disappears for the doping of 0.06 hole per unit cell. It is found that the nearestneighbor oxygen hopping destabilizes AF ground state which proves the importance of this parameter for quantitative analysis. A favorable comparison between the present results and those obtained within variational Monte Carlo, as well as within the Gutzwiller approximation for a similar model, is presented.

Insights into the structure of many-electron wave functions of Mott-insulating antiferromagnets: The three-band Hubbard model in full configuration interaction quantum Monte Carlo

“…Local spin-spin correlation function FCI |S i · S j | FCI (i = 1) (right) of the correlated i-FCIQMC wave function | FCI in the metallic RHF one-particle basis. Like previous studies [37][38][39][40][41][42], we find that the exact i-FCIQMC ground state establishes an antiferromagnetic long-range order across the copper sites, illustrated by the staggered magnetization, (Table I). Again, UHF theory reproduces this closely by separating α and β orbitals on two sublattices while yielding identical band structures for both channels.…”

Doping dependence of the electronic structure and magnetic order in high-Tcsuperconductors

“…The doping dependence of hole distribution and the fast disappearence of antiferromagnetic (AF) long-range order under doping 5 - 8 have been studied by means of different approaches, namely, the Hartree-Fock approximation, 9 the local ansatz method, 10 a mean-field approximation that includes the disorder introduced by holes, 11 and mean-field slave-boson techniques. 12 • 13 Also, in Ref.…”

Mixed Valence Quasiparticles in CuO2Planes

“…This approach has been successful in repro acing the quasiparticle (QP) bands in NiO [3] and the weakly dispersive states near the Fermi level (FL) in HTS [4]. The covalent character of the localized 3d9 states [5,6] motivated us to consider an extension of a strongly correlated SFM to a CuO2 plane which implements explicitly the mixed valence (MV) behaviour of the p and d-holes.We consider the four-band model for a CuO2 plane including Cu(3dx2_y2) (x), Cu(3d3z 2_ 1 ) (z), and O(2pσ) orbitals, and assume the weak Cu-O hybridization as compared with the Coulomb repulsion at Cu sites (It,, I <G U). Thus, we have integrated out the transitions to the lower Hubbard band (LHB) (3d8) [2] [which is split into one high-spin ( 3 A2) and two low-spin ( " A2, 1 E1) multiplets], while the upper Hubbard band (UHB) (3d 9 ), described by the projected operators, diσ = diσ(1ni,_ σ ), still hybridizes with 2p holes.…”

“…This approach has been successful in repro acing the quasiparticle (QP) bands in NiO [3] and the weakly dispersive states near the Fermi level (FL) in HTS [4]. The covalent character of the localized 3d9 states [5,6] motivated us to consider an extension of a strongly correlated SFM to a CuO2 plane which implements explicitly the mixed valence (MV) behaviour of the p and d-holes.…”