Landauer formula for interacting systems: a consistent non-perturbative approximation

TL;DR

This paper develops a non-perturbative approximation for the Landauer formula in interacting quantum systems, enabling more accurate transport calculations beyond traditional perturbation methods.

Contribution

It introduces a consistent, non-perturbative approximation for electric and thermal currents that extends the GW approximation while ensuring current conservation.

Findings

Captures important non-perturbative features

Provides a framework for systems where exact solutions are unavailable

Ensures current conservation with proper self-energy and vertex corrections

Abstract

Transport measurements are one of the most widely used methods of characterizing small systems in chemistry and physics. When interactions are negligible, the current through quantum dots, nanowires, molecular junctions, and other submicron structures can be obtained using the Landauer formula. Meir and Wingreen derived an exact expression for the current that also applies in the presence of interactions. This powerful theoretical tool requires knowledge of the exact Green's function. So far, an approximation extending beyond direct finite-order perturbation theory is missing. Here, we provide general expressions for both the electric and thermal currents where we expand the self-energy to the lowest order (frequently dubbed the GW approximation) but keep contributions to all orders in this quantity. Moreover, we show that the electric current is conserved only when the self-energy and vertex corrections are correctly included. We demonstrate that our formulae capture important non-perturbative features and hence, provide a powerful tool in cases where the exact solution cannot be found.