Second-order dual fermion approach to the Mott transition in the two-dimensional Hubbard model

TL;DR

This paper introduces a second-order dual fermion approach to study the Mott transition in the 2D Hubbard model, capturing nonlocal correlations and improving upon single-site methods.

Contribution

The work applies a second-order dual fermion approximation to effectively include nonlocal correlations in the Hubbard model's Mott transition analysis.

Findings

Reduces the critical interaction for the transition

Inverts the slope of transition lines compared to single-site DMFT

Shows smaller momentum differentiation than cluster methods

Abstract

We apply the dual fermion approach with a second-order approximation to the self-energy to the Mott transition in the two-dimensional Hubbard model. The approximation captures nonlocal dynamical short-range correlations as well as several features observed in studies using cluster dynamical mean-field theory. This includes a strong reduction of the critical interaction and inversion of the slope of the transition lines with respect to single-site dynamical mean-field theory. We show that these effects coincide with a much smaller momentum differentiation compared to cluster methods. We further discuss the role of the self-consistency condition and show that the approximation behaves as an asymptotic series at low temperature.