Efficient perturbation theory for quantum lattice models

TL;DR

This paper introduces a new ladder approximation method for dual fermions that improves convergence and accurately captures long-range correlations in quantum lattice models, specifically applied to the 2D Hubbard model.

Contribution

The paper presents a novel ladder approximation technique for dual fermions that enhances convergence and captures long-range correlations beyond traditional methods.

Findings

Improved convergence of perturbation series for dual fermions.

Suppression of the Neel temperature aligning with QMC results.

Effective distinction between short- and long-range correlations.

Abstract

We present a novel approach to long-range correlations beyond dynamical mean-field theory through a ladder approximation to dual fermions. The new technique is applied to the two-dimensional Hubbard model. We demonstrate that the transformed perturbation series for the nonlocal dual fermions has superior convergence properties over standard diagrammatic techniques. The critical Neel temperature of the mean-field solution is suppressed in the ladder approximation, in accordance with quantum Monte-Carlo (QMC) results. An illustration of how the approach captures and allows to distinguish short- and long-range correlations is given.