One-loop approximation for the Hubbard model

TL;DR

This paper develops a one-loop approximation method for the Hubbard model, deriving Green's functions and spectral properties that align with Monte Carlo results, enhancing understanding of strongly correlated electron systems.

Contribution

It introduces a diagram technique for the Hubbard model using site cumulants and derives an equation for Green's functions in a one-loop approximation for two-dimensional systems.

Findings

Four-band spectral structure consistent with Monte Carlo data

Spectral function shapes match observed features

Band maxima originate from different Brillouin zone regions

Abstract

The diagram technique for the one-band Hubbard model is formulated for the case of moderate to strong Hubbard repulsion. The expansion in powers of the hopping constant is expressed in terms of site cumulants of electron creation and annihilation operators. For Green's function an equation of the Larkin type is derived and solved in a one-loop approximation for the case of two dimensions, nearest-neighbor hopping and half-filling. The obtained four-band structure of the spectrum and the shapes of the spectral function are close to those observed in Monte Carlo calculations. It is shown that the maxima forming the bands are of a dissimilar origin in different regions of the Brillouin zone.