Perturbative theory of the non-equilibrium singlet-triplet transition

TL;DR

This paper develops a perturbative theoretical framework to analyze the non-equilibrium singlet-triplet transition in a two-level quantum dot, capturing key experimental phenomena including the Kondo effect.

Contribution

It introduces a perturbative approach within the Keldysh formalism to study equilibrium and non-equilibrium properties of quantum dots near the singlet-triplet transition, including spectral functions and conductance.

Findings

Perturbative method captures the Kondo effect in quantum dots.

Reproduces experimentally observed spectral and conductance features.

Applicable for moderate interaction strengths.

Abstract

We study equilibrium and non-equilibrium properties of a two-level quantum dot close to the singlet-triplet transition. We treat the on-site Coulomb interaction and Hund's rule coupling perturbatively within the Keldysh formalism. We compute the spectral functions and the differential conductance of the dot. For moderate interactions our perturbative approach captures the Kondo effect and many of the experimentally observed properties.