Symmetry breaking and restoration using the equation-of-motion technique for nonequilibrium quantum impurity models

TL;DR

This paper identifies symmetry violations in the equation-of-motion approach for nonequilibrium quantum impurity models and proposes a scheme to restore these symmetries, ensuring physically consistent results.

Contribution

It introduces a method to restore fundamental symmetry relations in the equation-of-motion technique for quantum impurity models.

Findings

Symmetry violations can cause unphysical behavior in the approach.

The proposed scheme successfully restores symmetry relations.

Illustrations demonstrate improved physical consistency in models.

Abstract

The description of the dynamics of correlated electrons in quantum impurity models is typically described within the nonequilibrium Green function formalism combined with a suitable approximation. One common approach is based on the equation-of-motion technique often used to describe different regimes of the dynamic response. Here, we show that this approach may violate certain symmetry relations that must be fulfilled by the definition of the Green functions. These broken symmetries can lead to unphysical behavior. To circumvent this pathological shortcoming of the equation-of-motion approach we provide a scheme to restore basic symmetry relations. Illustrations are given for the Anderson and double Anderson impurity models.