The renormalized superperturbation theory (SPT) approach to the Anderson model in and out of equilibrium

TL;DR

This paper reviews and extends the renormalized superperturbation theory for the Anderson model, focusing on out-of-equilibrium steady states and comparing results with NRG calculations.

Contribution

It introduces higher-order extensions of the renormalized SPT and clarifies the role of Ward identities in out-of-equilibrium calculations.

Findings

Higher-order results agree with NRG calculations

Extended SPT provides accurate descriptions of non-linear regimes

Clarifies theoretical foundations for out-of-equilibrium properties

Abstract

The properties of current-carrying steady states of strongly correlated systems away from the linear-response regime are of topical interest. In this article, we review the renormalized perturbation theory, or renormalized SPT of reference [1] for the Anderson model. We present an extension to higher orders and compare the higher-order results with NRG calculations. Finally, we elucidate the role of Ward identities in calculating out-of-equilibrium properties and address claims made in the literature.