Theoretical model for multi-orbital Kondo screening in strongly correlated molecules with several unpaired electrons

TL;DR

This paper develops a theoretical model to understand Kondo screening in molecules with multiple unpaired electrons, introducing concepts like Kondo orbitals and providing explanations for experimental observations.

Contribution

It presents a perturbative framework and numerical validation for multi-orbital Kondo screening, including the novel concept of Kondo orbitals.

Findings

The model explains the emergence of Kondo screening involving multiple molecular orbitals.

Numerical renormalization group confirms the Kondo regime predictions.

Application to real molecules shows good agreement with experimental data.

Abstract

The mechanism of Kondo screening in strongly correlated molecules with several unpaired electrons on a metal surface is still under debate. Here, we provide a theoretical framework that rationalizes the emergence of Kondo screening involving several extended molecular orbitals with unpaired electrons. We introduce a perturbative model, which provides simple rules to identify the presence of antiferromagnetic spin-flip channels involving charged molecular multiplets responsible for Kondo screening. The Kondo regime is confirmed by numerical renormalization group calculations. In addition, we introduce the concept of Kondo orbitals as molecular orbitals associated with the Kondo screening process, which provide a direct interpretation of experimental $dI/dV$ maps of Kondo resonances. We demonstrate that this theoretical framework can be applied to different strongly correlated open-shell molecules on metal surfaces, obtaining good agreement with previously published experimental data.