The one-particle Green's function of one.dimensional insulating materials

TL;DR

This paper investigates the single-particle spectral-weight function of the ionic Hubbard model at half filling, revealing a critical transition in the low-energy regime characterized by a change in the structure of the spectral function.

Contribution

The study provides the first detailed analysis of the abrupt regime change in the SWF of the ionic Hubbard model using cluster perturbation theory, linking it to experimental spectra.

Findings

SWF exhibits a jump from two-peak to four-peak structure at critical U

Inner peaks are flat bands with small dispersion

Outer peaks correspond to Hubbard band edges

Abstract

The single particle spectral-weight function (SWF) of the ionic Hubbard model at half filling is calculated in the cluster perturbation theory approximation. An abrupt change of regime in the low-energy region, near the chemical potential, is found at a critical value, $U_{c}$, of the coupling constant (Hubbard $U$). The SWF at the Fermi points $k_{F}$=$\pm{\pi}/2$ jumps, as $U$ increases, from a two-peak structure, the gap edges, to a four-peak structure accompanied by a (non-vanishing) minimum of the charge-gap. The two inner peaks of this structure show very small dispersion (flat bands) away from the Fermi points, whereas the outer peaks mark the edges of the Hubbard bands. No other signatures of abrupt change are detected in the SWF. The two regimes are physically realized in the angle-resolved photoelectron spectra of $(TaSe_{4})_{2}I$, and the blue-bronze $K_{0.3}MoO_{3}$, respectively.