Numerical results for the single-particle spectral weight A(p,\ensuremath{\omega}) and the density of states N(\ensuremath{\omega}) for a 4\ifmmode\times\else\texttimes\fi{}4 Hubbard model are presented. Both the half filled insulating state and the doped metallic state are considered. At half filling the numerical results are compared with the mean-field spin-density-wave single-particle spectral weight, and away from half filling with a renormalized quasiparticle band description. The relationship of these results to experimental photoemission, inverse photoemission, and angular-resolved measurements is discussed.
We show in this paper that the single-particle spectral-weight function (SWF) of the one-dimensional ionic Hubbard model at half filling exhibits critical behavior, as a function of the on-site repulsion
U, near the chemical potential. The calculation has been carried out within the framework of the cluster perturbation theory approach of Senechal et al., Phys. Rev. Lett 84, 522 (2000). As
U increases, the SWF at ${k}_{F}=\ifmmode\pm\else\textpm\fi{}\ensuremath{\pi}∕2$ (the Fermi points) jumps from the two-peak structure (plus two weak side peaks) characteristic of low
U<Uc to a four-peak structure beyond
Uc where all the peaks have about the same spectral weight. This abrupt spectral-weight transfer from the inner to the outer peaks can be traced to the ionic-neutral transition characteristic of this system and seems to correspond to the first critical point of the two-point scenario discussed in the literature. It is accompanied by a nonvanishing minimum of the single-particle charge gap. As
U increases further, the system evolves gradually into a Mott-Hubbard insulator. No other signatures of abrupt change are detected in the SWF. These results are discussed in the light of photoelectron spectroscopic measurements of quasi-one-dimensional materials.