Two-impurity Kondo effect in potassium doped single-layer p-sexiphenyl films

TL;DR

This study investigates the two-impurity Kondo effect in potassium-doped single-layer para-sexiphenyl films, revealing how Kondo singlet states evolve and compete with antiferromagnetic couplings, providing experimental insights into the two-impurity Kondo model.

Contribution

It presents the first experimental observation of the two-impurity Kondo effect in organic molecular films, demonstrating the evolution of Kondo and antiferromagnetic states with inter-molecular distance.

Findings

Kondo resonance observed near the Fermi level with a T_K of about 30 K.

Splitting of the Kondo peak depends on inter-molecular distance.

Antiferromagnetic singlet state is destroyed with increasing temperature.

Abstract

We show that a self-assembled phase of potassium (K) doped single-layer para-sexiphenyl (PSP) film on gold substrate is an excellent platform for studying the two-impurity Kondo model. On K-doped PSP molecules well separated from others, we find a Kondo resonance peak near EF with a Kondo temperature of about 30 K. The Kondo resonance peak splits when another K-doped PSP molecule is present in the vicinity, and the splitting gradually increases with the decreased inter-molecular distance, with no signs of phase transition. Our data demonstrate how a Kondo singlet state gradually evolves into an antiferromagnetic singlet state due to the competition between Kondo screening and antiferromagnetic RKKY coupling, as described in the two-impurity Kondo model. Intriguingly, the antiferromagnetic singlet is destroyed quickly upon increasing temperature and transforms back to a Kondo singlet well below the Kondo temperature. Our data provide a comprehensive picture and quantitative constraints on related theories and calculations of two-impurity Kondo model.