Kondo effect and spin quenching in high-spin molecules on metal substrates

TL;DR

This paper provides a detailed, parameter-free theoretical analysis of the Kondo effect in high-spin manganese phthalocyanine molecules on Pb(111), revealing asymmetric Kondo resonance and underscreened spin behavior.

Contribution

It offers a comprehensive, parameter-free understanding of the Kondo effect in high-spin molecules, clarifying the origin of asymmetric resonance and underscreened spin states.

Findings

Asymmetric Kondo resonance observed experimentally is explained by a single Kondo channel.

The second Kondo channel's spectral signature is suppressed due to singlet formation.

A spin-3/2 underscreened Kondo effect occurs due to lack of hybridization of one orbital.

Abstract

Using a state-of-the art combination of density functional theory and impurity solver techniques we present a complete and parameter-free picture of the Kondo effect in the high-spin ($S=3/2$) coordination complex known as Manganese Phthalocyanine adsorbed on the Pb(111) surface. We calculate the correlated electronic structure and corresponding tunnel spectrum and find an asymmetric Kondo resonance, as recently observed in experiments. Contrary to previous claims, the Kondo resonance stems from only one of three possible Kondo channels with origin in the Mn 3d-orbitals, its peculiar asymmetric shape arising from the modulation of the hybridization due to strong coupling to the organic ligand. The spectral signature of the second Kondo channel is strongly suppressed as the screening occurs via the formation of a many-body singlet with the organic part of the molecule. Finally, a spin-1/2 in the 3d-shell remains completely unscreened due to the lack of hybridization of the corresponding orbital with the substrate, hence leading to a spin-3/2 underscreened Kondo effect.