Non-equilibrium transport theory of the singlet-triplet transition: perturbative approach

TL;DR

This paper employs a simple iterative perturbation theory to analyze the non-equilibrium singlet-triplet transition in quantum dots, successfully reproducing key experimental features and revealing the robustness of the approach.

Contribution

It demonstrates that a straightforward perturbative method can effectively model complex non-equilibrium phenomena in quantum dots, including the ST transition and Kondo effects.

Findings

Reproduces experimental features of the ST transition

Identifies the importance of starting point in perturbation theory

Shows the perturbation theory's validity at relatively strong interactions

Abstract

We use a simple iterative perturbation theory to study the singlet-triplet (ST) transition in lateral and vertical quantum dots, modeled by the non-equilibrium two-level Anderson model. To a great surprise, the region of stable perturbation theory extends to relatively strong interactions, and this simple approach is able to reproduce all experimentally-observed features of the ST transition, including the formation of a dip in the differential conductance of a lateral dot indicative of the two-stage Kondo effect, or the maximum in the linear conductance around the transition point. Choosing the right starting point to the perturbation theory is, however, crucial to obtain reliable and meaningful results.